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9 Aug 1993

Volume 63, Issue 6, pp. 709-852

Page 1 of 3 Pages Next Page | Jump to Page

Band‐edge refractive optical nonlinearities in molecular beam‐grown ZnSe epilayers

J. A. Bolger, I. Galbraith, A. K. Kar, J. Simpson, S. Y. Wang, K. A. Prior, B. C. Cavenett, and B. S. Wherrett

Appl. Phys. Lett. 63, 709 (1993); http://dx.doi.org/10.1063/1.109935 (3 pages) | Cited 6 times

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We report novel measurements of the room temperature refractive optical nonlinearities in a molecular beam epitaxy‐grown ZnSe epilayer at frequencies near to the band edge. Time‐resolved changes in the transmission spectrum due to a two‐photon generated plasma of free carriers are monitored with a broad‐band white‐light continuum probe. The refractive index changes, measured for photon energies between 0.8 and 0.05 eV below the free‐exciton line at 2.68 eV, with photoexcited carrier densities of (2–5)×1018 cm−3, are found to be in good agreement with a many‐body plasma calculation.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Pc Optical bistability, multistability, and switching, including local field effects
78.66.Hf II-VI semiconductors
78.47.-p Spectroscopy of solid state dynamics

Theoretical gain of strained quantum well grown on an InGaAs ternary substrate

Hiroshi Ishikawa

Appl. Phys. Lett. 63, 712 (1993); http://dx.doi.org/10.1063/1.109936 (3 pages) | Cited 18 times

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Optical gain is calculated for a strained quantum well grown on a ternary In1−xGaxAs substrate which is now being developed. Using an In0.26Ga0.74As substrate we can design a strained quantum well for 1.3 μm laser with a large band gap InGaP or InGaAsP barrier layer. This gives a much deeper potential well when compared with that on an InP substrate and results in a high optical gain owing to the large subband energy separation provided by the deep well. The optical gain of the strained quantum well on the ternary substrate is shown to be higher by about 750 cm−1 when compared with that on an InP substrate.
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42.55.Px Semiconductor lasers; laser diodes
78.66.Fd III-V semiconductors
68.55.-a Thin film structure and morphology

Radiation trapping forces on microspheres with optical tweezers

W. H. Wright, G. J. Sonek, and M. W. Berns

Appl. Phys. Lett. 63, 715 (1993); http://dx.doi.org/10.1063/1.109937 (3 pages) | Cited 59 times

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Axial trapping forces exerted on microspheres are predicted using a Gaussian beam electromagnetic field model and a ray‐optics model, and compared with experimental measurements. Ray‐optics predicts a maximum trapping efficiency Q= −0.14 for optically trapped polystyrene microspheres in water, compared to a measured value of −0.12 ± 0.014 for 10 μm diam microspheres. When the microspheres are composed of amorphous silica, the predicted ray‐optics Q decreases to −0.11, compared to a Q = −0.034 predicted by the electromagnetic field model, and a measured value of −0.012 ± 0.001 for 1 μm diam microspheres. These results indicate that the two models have applicability in two different size regimes, and thus, are complementary.
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42.62.-b Laser applications
07.60.-j Optical instruments and equipment
87.80.-y Biophysical techniques (research methods)

Analysis of hydrogen diffusion from proton‐exchanged layers in LiNbO3

H. C. Casey, Chang‐Ho Chen, J. M. Zavada, and S. W. Novak

Appl. Phys. Lett. 63, 718 (1993); http://dx.doi.org/10.1063/1.109938 (3 pages) | Cited 9 times

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Hydrogen profiles for proton‐exchanged layers in Z‐cut LiNbO3 were obtained by secondary ion mass spectrometry measurements after annealing at 400 °C for times from 6 to 180 min. To fit the measured hydrogen profiles, it was necessary to use two separate Gaussian diffusion profiles which could be designated as a more slowly diffusing substitutional hydrogen on lithium sites and a more rapidly diffusing interstitial hydrogen. At 400 °C, analysis leads to a substitutional hydrogen diffusion coefficient Ds≊4.6×10−12 cm2/s and an interstitial hydrogen diffusion coefficient Di≊1.5×10−11 cm2/s.
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66.30.J- Diffusion of impurities
61.72.up Other materials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

New continuous wave infrared Ar‐Xe laser at intermediate gas pressures pumped by a transverse radio frequency discharge

Y. B. Udalov, P. J. M. Peters, M. B. Heeman‐Ilieva, F. H. J. Ernst, V. N. Ochkin, and W. J. Witteman

Appl. Phys. Lett. 63, 721 (1993); http://dx.doi.org/10.1063/1.109939 (2 pages) | Cited 8 times

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An atomic Xe laser with a transverse rf excitation has been operated in a cw mode in the intermediate pressure regime. The laser output spectrum consisted of 5 Xe lines with wavelengths of 2.03, 2.63, 2.65, 3.37, and 3.51 μm. The unoptimized total output power of 330 mW was obtained for a gas mixture Ar:He:Xe=59:40:1 at a pressure of 85 Torr and a rf input power of 150 W and excitation frequency of 121 MHz.  
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.-v Laser optical systems: design and operation

Ultrashort pulse reshaping using a semiconductor laser amplifier in a ring cavity

Patrick Langlois and Michel Piché

Appl. Phys. Lett. 63, 723 (1993); http://dx.doi.org/10.1063/1.109940 (3 pages) | Cited 1 time

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We describe an interferometric method for the reshaping and amplification of a mode‐locked train of short laser pulses, based on a ring cavity containing a semiconductor laser amplifier. The amplifying medium provides both the gain and the phase nonlinearity needed for pulse reshaping. Numerical simulations have shown that the best reshaping occurs with the use of a low finesse cavity operated at laser threshold. Upon these conditions, calculations have shown that both pulse compression and amplification are obtained over a broad range of values of the linear phase shift between the cavity and pulse train. Pulse amplification and compression factors exceeding 50 and 100, respectively, resulting in peak power amplification factors up to 1000, are predicted for a 25 dB amplifier. These factors can be increased by decreasing the ratio of the input pulse energy over the saturation energy of the amplifier.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Rz Doped-insulator lasers and other solid state lasers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking

Gain‐guided laser diode having a curved‐mirror‐cavity with a low astigmatism

A. Toda, T. Kobayashi, M. Dohsen, and Y. Mori

Appl. Phys. Lett. 63, 726 (1993); http://dx.doi.org/10.1063/1.109941 (3 pages) | Cited 1 time

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A gain‐guided laser diode having a curved‐mirror‐cavity that has coaxial mirrors and a fan‐shaped stripe structure has been fabricated by dry etching. Although gain guided, the laser has an astigmatism of 4.1 μm, which is very low compared to conventional laser’s. The threshold current of the laser is 35 mA, the longitudinal mode spectrum is multiple, and the transverse optical mode is fundamental. These results are comparable to conventional gain‐guided lasers. Etched mirror laser diodes with flat facets have been stably operated over 1500 h under automatic‐power control at a power of 3 mW/facet at 50 °C, without facet coating  
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation

Room‐temperature green laser emission of Er:LiYF4

R. Brede, T. Danger, E. Heumann, G. Huber, and B. Chai

Appl. Phys. Lett. 63, 729 (1993); http://dx.doi.org/10.1063/1.109942 (2 pages) | Cited 35 times

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We report the first demonstration of a green erbium‐doped crystal laser at room temperature. Excited with a pulsed dye laser, the erbium‐doped LiYF4 crystal emitted on the 4S3/2–4I15/2 ground state transition. As expected from fluorescence measurements, the emitted radiation was polarized parallel to the optical axis. Laser oscillation has also been observed in erbium‐doped Y3Al5O12 and Lu3Al5O12 crystals.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.-v Laser optical systems: design and operation

Effect of crystallographic orientation on ferroelectric properties of PbZr0.2Ti0.8O3 thin films

R. Ramesh, T. Sands, and V. G. Keramidas

Appl. Phys. Lett. 63, 731 (1993); http://dx.doi.org/10.1063/1.109943 (3 pages) | Cited 60 times

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We report on the effect of cooling rate on the crystallographic orientation and ferroelectric properties of PbZr0.2Ti0.8O3 (PZT) thin films grown on a lattice matched bottom electrode such as c‐axis oriented Y‐Ba‐Cu‐O (YBCO). The cooling rate from deposition temperature influences the crystallographic orientation of the ferroelectric c axis of the PZT film as well as the electrical properties of the YBCO bottom electrode. As the volume fraction of the ferroelectric phase with the c axis in the plane of the film becomes higher, the hysteresis loops become more rounded and the polarization values become smaller. Highly c‐axis oriented films, obtained by cooling from the growth temperature at 20 °C/min, show an almost square hysteresis loop with the largest polarization values.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.55.-a Thin film structure and morphology

Low‐energy oxygen ion bombardment effect on BaTiO3 thin films grown by multi‐ion‐beam reactive sputtering technique

C.‐J. Peng, H. Hu, and S. B. Krupanidhi

Appl. Phys. Lett. 63, 734 (1993); http://dx.doi.org/10.1063/1.109944 (3 pages) | Cited 2 times

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Low‐energy oxygen ion bombardment was employed to modify the physical properties of BaTiO3 thin films grown by the multi‐ion‐beam reactive sputtering technique. The bombardment effect was shown in terms of film morphology, dielectric properties, dc resistivity degradation, and current‐voltage characteristics. The results showed that oxygen ion bombardment can lead to denser morphology, a higher dielectric constant, a lower dissipation factor, slower dc resistivity degradation rate, and lower leakage current. The possible reasons for these improvements include the changes in void network structure, grain boundary structure, and defect structure of the films.
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61.80.Jh Ion radiation effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.15.Cd Deposition by sputtering

Vertical and lateral hole aluminum filling characteristics employing electron cyclotron resonance plasma sputtering with high magnetic field

S. Shingubara, N. Morimoto, S. Takehiro, Y. Matsui, I. Utsunomiya, Y. Horiike, and H. Shindo

Appl. Phys. Lett. 63, 737 (1993); http://dx.doi.org/10.1063/1.109945 (3 pages) | Cited 3 times

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Filling of submicrometer vertical and lateral holes was investigated by employing ECR (electron cyclotron resonance) aluminum sputtering with two times higher magnetic field than the usual condition of 875 G. Deep submicron contact holes with no adhesive metal layer were satisfactorily filled at 350 °C, which was a much lower temperature than conventional methods. Buried lateral trenches with 1‐μm depth were also completely filled at 300 °C. The filling mechanism is considered to be a cooperative effect of an enhanced diffusion by an ion bombardment effect, and the formation of dense aluminum islands at the inner wall which act as an adhesive layer.
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81.15.Cd Deposition by sputtering
85.40.Hp Lithography, masks and pattern transfer

Diamond nucleation on epitaxially grown Y‐ZrO2 layers on Si(100)

S. M. Kanetkar, A. A. Kulkarni, Anil Vaidya, R. D. Vispute, S. B. Ogale, S. T. Kshirsagar, and S. C. Purandare

Appl. Phys. Lett. 63, 740 (1993); http://dx.doi.org/10.1063/1.109946 (3 pages) | Cited 8 times

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Enhanced nucleation of polycrystalline diamond has been achieved on Si(100) with an epitaxial intermediate layer of yttria stabilized zirconia (Y‐ZrO2). The epitaxial Y‐ZrO2 layer was grown by pulsed excimer laser ablation and the diamond deposition was accomplished using the hot filament chemical vapor deposition method. The morphological, structural, and defect properties of the diamond crystallites are studied using the techniques of scanning electron microscopy, x‐ray diffraction, and laser Raman spectroscopy, respectively.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology

Effect of an eigenstrain on slow viscous flow of compressible fluid films

Paul E. Murray

Appl. Phys. Lett. 63, 743 (1993); http://dx.doi.org/10.1063/1.109922 (3 pages) | Cited 2 times

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We present a general formulation of the mechanics of slow viscous flow of slightly compressible fluid films in the presence of an eigenstrain. An eigenstrain represents a constrained volume change due to temperature, concentration of a dissolved species, or a chemical transformation. A silicon dioxide film grown on a silicon surface is an example of a viscous fluid film that is affected by a constrained volume change. We obtain a general expression for pressure in a fluid film produced by a surface chemical reaction accompanied by a volume change. This result is used to study the effect of an eigenstrain on viscous stress relaxation in fluid films.
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68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.55.-a Thin film structure and morphology

Controlled misfit dislocation nucleation in Si0.90Ge0.10 epitaxial layers grown on Si

G. Patrick Watson, Eugene A. Fitzgerald, Ya‐Hong Xie, Paul J. Silverman, Alice E. White, and Kenneth T. Short

Appl. Phys. Lett. 63, 746 (1993); http://dx.doi.org/10.1063/1.109923 (3 pages) | Cited 7 times

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Misfit dislocation formation has been controlled during growth at 500 °C in strained, 720 nm Si0.90Ge0.10 on Si. The Si substrates were selectively Ge+ ion implanted and etched to form a series of mesas with stripes of implant damaged crystal. Misfit dislocations nucleated preferentially from the ion implanted regions during epitaxial layer growth, while other nucleation sources were inhibited by the low growth temperature and the etched trenches between mesas. Films were relaxed by as much as 35%. The epitaxial layers on some mesas were relaxed in essentially one 〈110〉 direction as well. Electron beam induced current images indicate that ion‐implant activated misfit dislocations form before heterogeneous nucleation sources can operate, so that relaxation occurs in a more uniform manner.
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68.55.-a Thin film structure and morphology
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Fabrication of silicon nanostructures with a scanning tunneling microscope

E. S. Snow, P. M. Campbell, and P. J. McMarr

Appl. Phys. Lett. 63, 749 (1993); http://dx.doi.org/10.1063/1.109924 (3 pages) | Cited 89 times

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A technique is presented for fabricating Si nanostructures with a scanning tunneling microscope operated in air. The process involves the direct chemical modification of a H‐passivated Si(100) surface and a subsequent liquid etch. The chemically modified portions of the surface can withstand a deep (≳100 nm) liquid etch of the unmodified regions with no etch degradation of the modified surface. At a write speed of 1–10 μm/s, large‐area (50 μm×50 μm) patterns with lateral feature sizes ∼25 nm are reliably fabricated.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Tailoring of internal fields in InGaAs/GaAs multiwell structures grown on (111)B GaAs

A. S. Pabla, J. L. Sanchez‐Rojas, J. Woodhead, R. Grey, J. P. R. David, G. J. Rees, G. Hill, M. A. Pate, P. N. Robson, R. A. Hogg, T. A. Fisher, A. R. K. Willcox, D. M. Whittaker, M. S. Skolnick, and D. J. Mowbray

Appl. Phys. Lett. 63, 752 (1993); http://dx.doi.org/10.1063/1.109925 (3 pages) | Cited 41 times

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We present a study of internal field distributions in strained InGaAs/GaAs multiple quantum wells in p‐i‐n structures grown on (111)B‐oriented GaAs. Room temperature photocurrent spectroscopy shows clear blueshifting of the e1‐hh1 transition as the well fields are reduced by external bias. The relative length of total well to total barrier material is shown to be an important factor in determining the well and barrier fields. We demonstrate a photocurrent contrast ratio of 4.5:1 for only 3 V applied bias across a 25 quantum well In0.13Ga0.87As p‐i‐n diode and discuss the implication of our results to the design of high performance electro‐optic modulators and self electro‐optic effect devices in this material system.
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78.66.Fd III-V semiconductors
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.79.Hp Optical processors, correlators, and modulators

Dopant migration and lateral p‐n junctions in metalorganic vapor phase epitaxy of AlGaAs on nonplanar GaAs substrates

T. Y. Wang, L. S. Heath, and W. Stutius

Appl. Phys. Lett. 63, 755 (1993); http://dx.doi.org/10.1063/1.109898 (3 pages) | Cited 2 times

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Lateral p‐n junctions have been demonstrated in the low pressure metalorganic vapor phase epitaxial growth of AlGaAs structures on nonplanar GaAs substrates. It is shown that the final distribution of dopant atoms is governed by the dopant migration over the structured surface evolving during the growth. This result has allowed the single‐step growth of index‐guided lasers with a built‐in lateral current confinement scheme.
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68.55.-a Thin film structure and morphology
42.55.Px Semiconductor lasers; laser diodes

Ion beam mixing for enhanced electron tunneling in metal‐oxide‐silicon structures

A. J. Walker and J. Politiek

Appl. Phys. Lett. 63, 758 (1993); http://dx.doi.org/10.1063/1.109899 (3 pages)

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Metal‐oxide‐silicon (MOS) structures were fabricated to investigate enhanced Fowler–Nordheim tunneling in thin oxides due to ion beam mixing. Ions of germanium were implanted into a 100 nm polycrystalline silicon layer deposited on 10 nm thermal silicon dioxide such that the tail of the implant profile contains the thin oxide. Besides simple MOS capacitors and transistors, flash electrically erasable programmable read only memory (flash EEPROM) cells were fabricated for the first time using this technique. Using 1×1015 cm−2 at 80 keV the Fowler–Nordheim tunneling barrier reduced by about 0.9 eV at the polycrystalline gate/oxide interface and by 1.3 eV at the oxide/substrate interface. The consequently lower program/erase voltages in the flash EEPROM were measured. Flash EEPROM charge retention measurements show that the discharge process is logarithmic in time. This leads to the possibility of flash EEPROMs being programmed and erased at low voltages and having sufficient charge retention for several years operation.
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73.40.Gk Tunneling
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.80.Jh Ion radiation effects
85.30.Tv Field effect devices

Segregation of Si δ doping in GaAs‐AlGaAs quantum wells and the cause of the asymmetry in the current‐voltage characteristics of intersubband infrared detectors

H. C. Liu, Z. R. Wasilewski, M. Buchanan, and Hanyou Chu

Appl. Phys. Lett. 63, 761 (1993); http://dx.doi.org/10.1063/1.109900 (3 pages) | Cited 47 times

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Dopant segregation in the well region of a multiple quantum well intersubband photodetector can cause an asymmetry in the observed forward and reverse current‐voltage characteristics. We compensate for the segregation by shifting the position of the Si δ doping in the well and model the effect with good agreement for a range of shift values. For samples grown at a substrate temperature of 605 °C, we find that the observed behavior is best described by assuming that the Si δ‐doping profile smears in the growth direction resulting in an asymmetric broadening of about 27 Å.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.66.Fd III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Nano edge roughness in polymer resist patterns

Toshiyuki Yoshimura, Hiroshi Shiraishi, Jiro Yamamoto, and Shinji Okazaki

Appl. Phys. Lett. 63, 764 (1993); http://dx.doi.org/10.1063/1.109901 (3 pages) | Cited 47 times

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Ultrasmall edge roughness in delineated patterns (nano edge roughness) is investigated in nanostructures made of negative‐type electron beam polymer resists by atomic force microscope measurements. Very narrow isolated lines 10–20 nm wide are fabricated with a finely focused electron beam provided by a scanning electron microscope. A chemical amplification novolak resin‐based resist shows nano edge roughness which cannot be neglected in nanofabrication. To investigate the origin of the roughness, conventional two‐component resist systems are microscopically compared. An azide polyvinylphenol‐based resist and an azide novolak resin‐based resist are used. The novolak resin‐based resist exhibits a rougher surface than the polyvinylphenol‐based one. This result suggests that the polymer structures of the base resins cause nano edge roughness of a chemical amplification resist in connection with the acid diffusion during the post‐exposure bake process.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Photoinduced current transient spectroscopy of boron doped diamond

J. W. Glesener

Appl. Phys. Lett. 63, 767 (1993); http://dx.doi.org/10.1063/1.109902 (3 pages) | Cited 13 times

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A Schottky device fabricated on a natural type 2b diamond was characterized using photoinduced current transient spectroscopy (PICTS). A trapping level, presumed to be due to boron, with an activation energy of 0.29 eV was found from PICTS. Resistance measurements on the same device produced an activation energy of 0.38 eV. The two methods, while being described by the same exponential temperature dependence, have prefactors with different physical origins. Since the activation energy measured by PICTS is proportional to σeffe−E/kT, the difference in the measured values could be attributed to a temperature dependence in the ‘‘effective’’ hole capture cross‐section σeff. This report also demonstrates the potential of PICTS in identifying an electrically active trap in a sample whose high series resistance renders it difficult to characterize using capacitance based methods.
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71.55.Cn Elemental semiconductors
72.80.Cw Elemental semiconductors
72.40.+w Photoconduction and photovoltaic effects

Electrically induced light emission and novel photocurrent response of a porous silicon device

Hongtao Shi, Youdou Zheng, Yongbin Wang, and Renkuan Yuan

Appl. Phys. Lett. 63, 770 (1993); http://dx.doi.org/10.1063/1.109903 (3 pages) | Cited 9 times

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An electrically induced visible light emitting porous silicon (PS) device was fabricated by laterally anodizing an n‐type single‐crystal silicon (Si) wafer. Al/PS Schottky junctions exhibited rectifying I‐V characteristics with an ideality factor of 7. The intensity of current‐induced light emission increased with applied electrical current. Novel photocurrent spectra of the device under different reverse biases were measured at room temperature and reported for the first time, which showed three peaks of light absorption pertinent to the quantized energy levels of the PS. Interpretation is given based on the quantum confinement model.  
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78.55.Hx Other solid inorganic materials
78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
73.40.Ei Rectification

Piezoelectric‐induced current asymmetry in [111] InGaAs/InAlAs resonant tunneling diodes for microwave mixing

J. M. Hernández, I. Izpura, E. Calleja, and E. Muñoz

Appl. Phys. Lett. 63, 773 (1993); http://dx.doi.org/10.1063/1.110777 (3 pages) | Cited 6 times

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This letter predicts a strong nonlinear current density versus voltage (J‐V) dependence in InAlAs/InGaAs/InAlAs double barrier resonant tunneling diodes (DBRTDs) with a strained well, grown on [111] InP. The piezoelectric field generates accumulation and depletion regions in both contact layers at zero bias, producing a high asymmetric J‐V characteristic while keeping a low device series resistance. Very high cutoff frequency devices, suitable for low‐level microwave mixing applications, are then proposed.
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73.40.Gk Tunneling
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.De Semiconductor-device characterization, design, and modeling

Normal incidence infrared modulator using direct–indirect transitions in GaSb quantum wells

H. Xie and W. I. Wang

Appl. Phys. Lett. 63, 776 (1993); http://dx.doi.org/10.1063/1.109904 (3 pages) | Cited 21 times

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We propose a novel normal incidence infrared modulator using the direct–indirect transitions induced by an applied electric field in GaSb quantum wells (QWs). The device is based on the principles that the quantum‐confined Stark shift is proportional to the effective mass, and that the interconduction subband absorption at normal incidence is forbidden in direct‐gap QWs but allowed in indirect‐gap QWs. Since the effective mass of the L valleys is larger than that of the Γ valley, the corresponding Stark shift is also larger. As a result, the ground state of a QW associated with the Γ point at zero voltage becomes L state under bias (direct–indirect transition). Consequently the device switches from being transparent to normal incidence light to strongly absorbing it. Based on our calculations for a GaSb/Ga0.5Al0.5Sb QW with a well width of 85 Å, changes in absorption coefficients up to 104 cm−1 in the modulation wavelength range of 14–18 μm could be achieved under an electric field in the range of 200 kV/cm. This is the most effective mechanism ever reported for normal incidence infrared modulators.  
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42.79.Hp Optical processors, correlators, and modulators
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Determination of the density of states at the Fermi level of hydrogenated amorphous silicon in thin‐film transistor structure by space charge limited current measurement

Hoe Sup Soh, Choochon Lee, Jin Jang, Moon Youn Jung, and Soon Sung Yoo

Appl. Phys. Lett. 63, 779 (1993); http://dx.doi.org/10.1063/1.109905 (3 pages) | Cited 3 times

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We studied the space charge limited current effect in hydrogenated amorphous silicon (a‐Si:H) thin‐film transistors (TFTs). We demonstrate that the drain current is space charge limited when the source‐drain voltage is large and the gate voltage is small. Using this space charge limited current we determined the density of states in the gap of a‐Si:H in a‐Si:H TFT.  
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85.30.Tv Field effect devices
73.61.Jc Amorphous semiconductors; glasses
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
71.23.-k Electronic structure of disordered solids
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