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23 Aug 1993

Volume 63, Issue 8, pp. 1017-1154

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Special narrowing of ultrashort laser pulses by self‐phase modulation in optical fibers

M. Oberthaler and R. A. Höpfel

Appl. Phys. Lett. 63, 1017 (1993); http://dx.doi.org/10.1063/1.109820 (3 pages) | Cited 42 times

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We demonstrate experimentally and theoretically that frequency‐modulated femtosecond laser pulses can be spectrally narrowed by self‐phase modulation in optical fibers. We obtain a reduction of the spectral linewidth from 10.6 down to 2.7 nm, limited only by the laser power in the fiber. Applications for extracavity conversion of femtosecond lasers to narrow‐linewidth picosecond sources are discussed.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.81.Dp Propagation, scattering, and losses; solitons

Light detection sensitivity of a vertical cavity structure used in an optical switch device

Yutaka Yamanaka, Takahiro Numai, Kenichi Kasahara, and Keiichi Kuboto

Appl. Phys. Lett. 63, 1020 (1993); http://dx.doi.org/10.1063/1.109821 (3 pages) | Cited 4 times

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The light detection characteristics in a vertical cavity surface‐emitting laser‐type vertical‐to‐surface transmission electrophotonic device (VC‐VSTEP) have been evaluated. To realize a low energy optical interconnection, not only the switching threshold energy but also the light detection sensitivity must be optimized. Maximum sensitivity is achieved when the input light wavelength and the field distribution coincide with fundamental cavity mode characteristics. Under the best matching condition, the input light energy necessary to switch the VC‐VSTEP state is easily lower than 1 pJ.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
78.66.Fd III-V semiconductors

Space‐ and time‐resolved investigation of short wavelength x‐ray laser in Li‐like Ca ions

Zhizhan Xu, Pinzhong Fan, Lihuang Lin, Yaolin Li, Xiaofang Wang, Peixiang Lu, Ruxin Li, Shensheng Han, Lan Sun, Aidi Qian, Baifei Shen, Zhiming Jiang, Zhengquan Zhang, and Jinzhi Zhou

Appl. Phys. Lett. 63, 1023 (1993); http://dx.doi.org/10.1063/1.109822 (3 pages) | Cited 6 times

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We have demonstrated the soft x‐ray amplification for lithium‐like Ca17+ 4f‐3d transition at 57.7 Å with 900 ps, 1.05 μm drive laser pulse. The spatial distribution of the gain coefficient and temporal history of the lasing line emissions were also obtained.
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42.55.Vc X- and γ-ray lasers
42.60.-v Laser optical systems: design and operation

High‐resolution line‐Q measurements of velocity‐selective nonlinear Faraday rotation in Rb vapor

W. D. Lee, J. J. Heuring, J. C. Campbell, W. F. Buell, and C. L. Davis

Appl. Phys. Lett. 63, 1026 (1993); http://dx.doi.org/10.1063/1.109823 (3 pages) | Cited 1 time

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Optical feedback from velocity‐selective nonlinear Faraday rotation in alkali metal vapors has been shown to be an effective technique for simultaneously stabilizing the frequency and reducing the linewidth of AlxGa1−xAs/GaAs lasers. The ultimate frequency stability of such a laser is limited by the quality factor Q=ν0/Δν of this frequency reference. In this letter we report the measurement of Q=6×106 for optical feedback from velocity‐selective nonlinear Faraday rotation in Rb vapor.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Epitaxial MgO on GaAs(111) as a buffer layer for z‐cut epitaxial lithium niobate

D. K. Fork and G. B. Anderson

Appl. Phys. Lett. 63, 1029 (1993); http://dx.doi.org/10.1063/1.109824 (3 pages) | Cited 35 times

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The epitaxial system z‐lithium niobate on GaAs(111)A and GaAs(111)B has been demonstrated by in situ pulsed laser deposition both with and without intermediate layers of MgO(111). The in‐plane epitaxial relationships are LiNbO3[110]∥GaAs[211] and [211] indicating the existence of 180° boundaries in the LiNbO3 both with and without the MgO layer, which grows cube‐on‐cube with the GaAs. Out‐of‐plane texture is typically 1.0° and 1.2° for the MgO and LiNbO3 layers, respectively. In‐plane texture is typically 2.8° and 4.5° for the MgO and LiNbO3 layers, respectively. This epitaxial system may be useful for monolithic electro‐optic or frequency doubling applications in conjunction with semiconductor laser diodes.
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68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

45‐cm long compression‐molded polymer‐based optical bus

Ray T. Chen, Suning Tang, Tomasz Jannson, and Joanna Jannson

Appl. Phys. Lett. 63, 1032 (1993); http://dx.doi.org/10.1063/1.109825 (3 pages) | Cited 5 times

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We report the formation of an optical bus using compression‐molding technique. The linear dimension of such a waveguide is well beyond that of a microlithographically defined waveguide. Theoretical calculation based on the effective index method was used to determine the optimal dimension of the molding tool design for single‐ and multimode waveguides. A molded photolime gel‐based polymer optical bus with a linear dimension of 45 cm was fabricated and then tested at 0.6328‐μm wavelength. Waveguide propagation loss from 0.5 to 2 dB/cm was determined using the two prism method. As a result of this long interconnection distance, board‐to‐board optical interconnects through backplane can be realized using the technology.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer

Real‐time in situ detection of SF6 in a plasma reactor

H. C. Sun and E. A. Whittaker

Appl. Phys. Lett. 63, 1035 (1993); http://dx.doi.org/10.1063/1.109826 (3 pages) | Cited 5 times

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We report on the real‐time in situ detection of SF6 in a plasma etching reactor with μTorr sensitivity using a tunable diode laser absorption spectrometer. The spectrometer employs combined wavelength and frequency modulation of the laser diode, an approach which allows for sensitive, interference fringe‐free detection of the SF6. The dual modulation scheme also provides a feedback signal which enables the laser to be frequency locked to the absorption line.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.Pi High-frequency and RF discharges

Electrical properties of strontium titanate thin films by multi‐ion‐beam reactive sputtering technique

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

Appl. Phys. Lett. 63, 1038 (1993); http://dx.doi.org/10.1063/1.109827 (3 pages) | Cited 17 times

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Thin films of SrTiO3 were deposited by multi‐ion‐beam reactive sputtering technique using SrO and Ti‐metal targets. The dielectric behavior of the films deposited on Pt‐coated Si substrates showed thickness dependence. A dielectric constant of 219 at 100 KHz was found for 1.2 μm thick films. A charge storage density of about 15 fC/μm2 and leakage current density of 106 μA/cm2 at an electric field of 0.17 MV/cm were obtained for 0.3 μm films. The probable interface layers present between film and silicon substrate, in the case of metal‐insulator‐silicon configuration, appear to influence the electrical behavior. Preliminary analysis showed that the conduction of the films in high field region was bulk‐limited Poole–Frenkel emission mechanisms.  
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.15.Cd Deposition by sputtering

Shallow angle lapping of III‐V semiconductor thin layer structures by an ion beam/chemical etching technique

D. W. Eckart and L. M. Casas

Appl. Phys. Lett. 63, 1041 (1993); http://dx.doi.org/10.1063/1.109828 (3 pages)

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Layer thicknesses of <2 nm have been resolved in GaAs‐AlGaAs superlattice structures using a novel method involving the chemical etching of the shallow lapped area surrounding an ion beam sputter crater formed after Auger electron spectroscopy depth profiling. This method can be used to measure layer thickness variations across a wafer of a nominal 15 nm InGaAs layer in a pseudomorphic high electron mobility transistor. It can also be used to probe interlayer lattice mixing at selected areas on the wafer, for example, near an ohmic contact.
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68.55.-a Thin film structure and morphology
81.65.-b Surface treatments

Measurement of residual stress in MgO thin films on GaAs by electron microscopy

Marc De Graef and David R. Clarke

Appl. Phys. Lett. 63, 1044 (1993); http://dx.doi.org/10.1063/1.109829 (3 pages) | Cited 5 times

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The residual stress in thin films of MgO deposited on GaAs is determined from the shape of characteristic diffraction bend contours, seen in the transmission electron microscope, in regions where the substrate was preferentially etched away leaving only the film. The residual stress in a MgO film deposited, by electron beam evaporation, at 450 °C, was found to be compressive with a magnitude of 176±8 MPa. This is opposite in sign to that expected on the basis of the thermal expansion and lattice mismatches.
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68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties

Improvement of InP/InGaAs heterointerfaces grown by gas source molecular beam epitaxy

Takayoshi Anan, Shigeo Sugou, Kenichi Nishi, and Toshinari Ichihashi

Appl. Phys. Lett. 63, 1047 (1993); http://dx.doi.org/10.1063/1.110765 (3 pages) | Cited 32 times

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Surface modification of a P2 beam‐exposed InGaAs surface and an As2 beam‐exposed InP surface was studied in situ using reflection high energy electron diffraction during gas source molecular beam epitaxy. It is revealed that the InP surface remained stable under As2 beam exposure after forming an InAs surface layer a few monolayers thick; the InGaAs surface became rough by P2 beam exposure. This surface roughening originates from substitutions of As to P atoms around Ga atoms. These substitutions result in the fairly reactive nature of the InGaAs surface under P2 beam exposure. From this viewpoint, we have proposed a new switching sequence which excludes surface gallium atoms by depositing one monolayer of In on the InGaAs surface before P2 beam exposure. This sequence drastically improves heterointerface quality, which was confirmed by an increase in photoluminescence intensity in InGaAs/InP short period superlattices.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Low‐temperature deposition of ferroelectric Bi4Ti3O12 films by the reactive ionized cluster beam method

Norio Kaneko, Keisuke Yamamoto, and Takeo Tsukamoto

Appl. Phys. Lett. 63, 1050 (1993); http://dx.doi.org/10.1063/1.109830 (3 pages)

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Using the reactive ionized cluster beam method, ferroelectric Bi4Ti3O12 is deposited at a low temperature. This method utilizes ionized and accelerated Bi and Ti clusters. Under optimum conditions, c‐axis oriented films can be formed on quartz and on Si(100) substrates at 200 and 250 °C, respectively. The crystal orientation can be controlled without changing the substrate material and temperature. Furthermore, it is found that the ionization and acceleration conditions of the Bi and Ti elements are responsible, respectively, for the BIT formation and its orientation. The dielectric constant of the films is 135 at 100 kHz and the spontaneous polarization is 4.2 μC/cm2. These ferroelectric properties are almost identical to the bulk material.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity

Low‐temperature synthesis of BaTiO3 thin films on silicon substrates by hydrothermal reaction

R. R. Bacsa, J. P. Dougherty, and L. J. Pilione

Appl. Phys. Lett. 63, 1053 (1993); http://dx.doi.org/10.1063/1.109831 (3 pages) | Cited 22 times

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Crystalline BaTiO3 thin films (0.2–1 μm) of dielectric constant 450–500 have been synthesized by the hydrothermal reaction of a titanium film (∼1 μm thickness) deposited on a silicon substrate with Ba(OH)2 solution (concentration 0.4 M) in the temperature range 100–200 °C. The reaction of the silicon substrate with the Ti film was prevented by deposition of a buffer layer of amorphous TiC between the Ti film and the Si substrate. The TiC not only prevented the diffusion of Si through the Ti layer but also allowed some reaction between itself and the Ti layer so that the adherence of the films was not degraded.
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68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.05.Bx Metals, semimetals, and alloys
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Thermal stability of the unstable fcc‐Fe50Cu50 phase prepared by mechanical alloying

J. Z. Jiang, U. Gonser, C. Gente, and R. Bormann

Appl. Phys. Lett. 63, 1056 (1993); http://dx.doi.org/10.1063/1.109832 (3 pages) | Cited 37 times

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An unstable fcc‐Fe50Cu50 alloy has been prepared by milling of elemental powder blends. The structure and the decomposition behavior of the alloy were studied by x‐ray diffraction and Mössbauer spectroscopy. A broad distribution of different local environments of the iron atoms was observed in the fcc‐FeCu phase. This indicates that Fe and Cu are mixed on an atomic level. In the initial state of decomposition, iron atoms precipitated coherently in the fcc‐FeCu matrix as fcc‐Fe particles. At higher annealing temperatures the particle size increased during the thermal treatment, and the fcc‐Fe precipitates transformed into the bcc‐Fe structure.
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81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.30.Bx Phase diagrams of metals, alloys, and oxides

Quantum wires prepared by molecular beam epitaxy regrowth on patterned AlGaAs buffer layers

K. Eberl, P. Grambow, A. Lehmann, A. Kurtenbach, K. v. Klitzing, D. Heitmann, M. Dilger, and M. Hohenstein

Appl. Phys. Lett. 63, 1059 (1993); http://dx.doi.org/10.1063/1.109833 (3 pages) | Cited 9 times

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Modulation doped GaAs quantum wires are prepared by molecular beam epitaxy regrowth on patterned AlGaAs buffer layers. The structural properties are investigated by scanning electron microscopy and by transmission electron microscopy. Far‐infrared spectroscopy provides information about the lateral confinement and the carrier density in the quantum wires. The measurements indicate a distinct dependence of the electronic width on the orientation of the quantum wires within the (100) plane. Confinement energies of 6.9, 9.3, and 11.7 meV are determined for the [011], [001], and the [011] wire orientations, respectively.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.30.Fs III-V and II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Ballistic‐electron‐emission microscopy of (100)CoGa/n‐type GaAs interfaces grown by molecular beam epitaxy

Liming Tsau, T. C. Kuo, and K. L. Wang

Appl. Phys. Lett. 63, 1062 (1993); http://dx.doi.org/10.1063/1.110774 (3 pages) | Cited 2 times

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A scanning tunneling microscope (STM) was used for the first time to investigate the (100)CoGa/GaAs interfaces grown by molecular beam epitaxy. The surface image indicates a vertical variation of about 7.5 Å with some domains of dimensions of about 170 Å. Furthermore, ballistic‐electron‐emission‐microscopy spectra of this metal/semiconductor interface show two turn‐on voltages, which account for the change of transmission probabilities for electrons with energies above the L minima and X minima of GaAs, respectively. The transmission into the X valleys of GaAs is found to be relatively stronger than that into the L valleys. This is explained by the CoGa band structure and the conservation of energy and transverse momentum for ballistically injected electrons. So far no ballistic electron current flowing into the Γ valley has been observed. For this reason, Schottky barrier height and its spatial variation measured by STM were not directly from the anticipated turn‐on voltage at the Γ minimum, but instead, from the thresholds corresponding to transmission into higher valleys.
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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
68.55.-a Thin film structure and morphology
73.30.+y Surface double layers, Schottky barriers, and work functions
73.20.At Surface states, band structure, electron density of states

Effect of back contact impedance on frequency dependence of capacitance‐voltage measurements on metal/diamond diodes

V. Venkatesan, K. Das, J. A. von Windheim, and M. W. Geis

Appl. Phys. Lett. 63, 1065 (1993); http://dx.doi.org/10.1063/1.109834 (3 pages) | Cited 17 times

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Differential capacitance‐voltage (C‐V) measurements were performed on Al and Pt rectifying contacts fabricated on natural (type IIb) diamonds. The C‐V data showed frequency dependence, which decreased significantly after reducing the back contact impedance. The frequency dependence seems primarily to be an effect of the contact capacitance, contact resistance, and bulk resistance of diamond. A model which includes these variables has been proposed to explain this frequency dependence using both large and small back contact impedances.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ei Rectification
73.40.Ns Metal-nonmetal contacts

Normal incidence infrared photodetectors using intersubband transitions in GaSb L‐valley quantum wells

Y. Zhang, N. Baruch, and W. I. Wang

Appl. Phys. Lett. 63, 1068 (1993); http://dx.doi.org/10.1063/1.109835 (3 pages) | Cited 35 times

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We report on the demonstration of normal incidence (IR) detectors based on interconduction subband transitions in narrow GaSb/Ga0.6Al0.4Sb0.9As0.1 multiquantum wells in which L valley is the ground state. Strong IR absorption at 7.8 μm with an absorption coefficient of 9100 cm−1 and good photodetector response covering a wide spectrum region have been achieved. The orientation dependence of the absorption is also presented. Our results indicate the potential of this novel structure for use as normal incidence IR photodetectors.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Ion channeling effect on lattice relaxation in strained In1−xGaxAs/InP multiple‐quantum‐well structure

Yukimi Takahashi, K. Kuriyama, Y. Matsui, and T. Kamijoh

Appl. Phys. Lett. 63, 1071 (1993); http://dx.doi.org/10.1063/1.109836 (3 pages) | Cited 2 times

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The ion channeling phenomena for the strained and strain partially relaxed In1−xGaxAs/InP multiple‐quantum‐well (MQW) structures, which are grown by metalorganic vapor phase epitaxy, are presented. In addition to a well‐known channeling phenomenon of strained‐layer MQW structures, which cause an enhanced dechanneling along 〈110〉, it was found that dechanneling in the substrate covered with strained MQW structure is enhanced in comparison with the strain partially relaxed MQW structure. This phenomenon is observed clearly for the 〈100〉 oriented substrate rather than that along the inclined 〈110〉 axis. It is suggested that a distortion perpendicular to the 〈100〉 growth direction is induced near the interface between the buffer layer and the MQW structure by the strain stored in MQW structure. This effect is less observed in the strain partially relaxed MQW structure than in the strained MQW structure.
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68.55.-a Thin film structure and morphology
61.85.+p Channeling phenomena (blocking, energy loss, etc.)

Er luminescence centers in GaAs grown by migration‐enhanced epitaxy

Akihito Taguchi, Minoru Kawashima, Kenichiro Takahei, and Yoshiji Horikoshi

Appl. Phys. Lett. 63, 1074 (1993); http://dx.doi.org/10.1063/1.109837 (3 pages) | Cited 7 times

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Er‐doped GaAs has been grown by migration‐enhanced epitaxy. The samples were grown at 300, 400, and 500 °C. Secondary ion mass spectroscopy measurements showed that the Er concentration in the grown epitaxial layer does not depend on the growth temperature between 300 and 500 °C. All samples showed luminescence due to the Er intra‐4f‐shell transition from the 4I13/2 excited state to the 4I15/2 ground state, but the spectra change drastically when the growth temperature is increased from 300 °C to 400 or 500 °C. The photoluminescence spectra of the samples grown above 400 °C are simpler than that of the sample grown at 300 °C. The spectrum of the sample grown at 300 °C became broad after annealing, whereas the spectra of the samples grown at 400 °C and above showed only changes in the relative intensity of the main luminescence lines. Some thermally stable Er luminescence centers seem to be preferentially formed at 400 and 500 °C.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.55.Cr III-V semiconductors

Prebreakdown conduction in zinc oxide varistors: Thermionic or tunnel currents and one‐step or two‐step conduction processes

M. S. Castro and C. M. Aldao

Appl. Phys. Lett. 63, 1077 (1993); http://dx.doi.org/10.1063/1.109838 (3 pages) | Cited 14 times

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This letter is aimed at understanding the intergranular conduction in zinc oxide varistors. In particular, we have studied current‐voltage and Arrhenius plots of the resistive current for the prebreakdown conduction. A current‐temperature (I‐T) relation has been found to present two breaks at ∼370 and ∼240 K. Although this result can be interpreted as a consequence of distinct regimes, we found that experimental I‐T curves can be theoretically reproduced by calculating currents for a double Schottky barrier. Experimental results were fitted with one‐ and two‐step transport process models. It was found that a two‐step model better reproduces the electrical properties of these devices.
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72.80.-r Conductivity of specific materials
71.55.-i Impurity and defect levels
73.30.+y Surface double layers, Schottky barriers, and work functions

Dopant compensation effects on impurity trapping and electrical resistivity of ion implanted amorphous silicon

S. Coffa and J. M. Poate

Appl. Phys. Lett. 63, 1080 (1993); http://dx.doi.org/10.1063/1.109839 (3 pages) | Cited 2 times

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The implantation of B and P in ion‐implanted amorphous Si has been investigated by measurements of spreading resistance and depth distribution of Pd trapped at defects. For concentrations of B or P in the range 0.2–1 at. %, the resistivity is reduced by an order of magnitude and the Pd trapping is retarded by the presence of B and enhanced by P. When B and P are present together at comparable concentrations the resistivity and the trapping efficiency of amorphous Si return to the undoped value. These compensation effects are explained in terms of the dopants changing the Fermi level position and hence the charge state and trapping efficiency of the defects. It is argued that most of the defects (∼1 at. %) are chargeable. These results provide a clue for understanding the dopant compensation phenomena observed in the rate of epitaxial crystallization of amorphous Si.
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61.72.up Other materials
61.72.Yx Interaction between different crystal defects; gettering effect
71.55.Jv Disordered structures; amorphous and glassy solids
72.80.Ng Disordered solids

Fermi level dependence of the ambipolar diffusion length in amorphous silicon thin film transistors

R. Schwarz, F. Wang, and M. Reissner

Appl. Phys. Lett. 63, 1083 (1993); http://dx.doi.org/10.1063/1.109840 (3 pages) | Cited 7 times

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The steady‐state photocarrier grating technique was applied to measure the ambipolar diffusion length (Lamb) in a‐Si:H thin film transistors. With this device we studied the Fermi level dependence of Lamb through the variation of the gate voltage. The experimental results show that Lamb decreases whereas the photoconductivity increases with positive gate voltage. We simulated the Fermi level dependence of electron and hole mobility‐lifetime products and found good agreement with the measured diffusion length.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Pz Photoconduction and photovoltaic effects
73.61.Jc Amorphous semiconductors; glasses
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Large observed exciton shifts with electric field in InGaAs/InGaAsP stepped quantum wells

T. Tütken, B. J. Hawdon, M. Zimmermann, A. Hangleiter, V. Härle, and F. Scholz

Appl. Phys. Lett. 63, 1086 (1993); http://dx.doi.org/10.1063/1.109814 (3 pages) | Cited 6 times

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We report the experimental realization of asymmetric stepped InGaAs/InGaAsP quantum wells. The structure was designed to optimize the quantum‐confined Stark shift. We have observed a shift of 30 meV in the heavy hole exciton absorption peak over an electric field change of 50 kV/cm. This shift is double that observed for the same structure without the stepped wells.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.30.Fs III-V and II-VI semiconductors

Carrier transport and intersubband population inversion in coupled quantum wells

W. M. Yee, K. A. Shore, and E. Schöll

Appl. Phys. Lett. 63, 1089 (1993); http://dx.doi.org/10.1063/1.109815 (3 pages) | Cited 15 times

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We theoretically study the possibility of achieving intersubband population inversion in coupled GaAs quantum wells, taking into account the relevant physical mechanisms of resonant tunneling and intersubband emission‐absorption processes. Two coupled quantum well structures having intersubband resonant wavelengths of 10 and 60 μm are considered. We find that, in the case of an operating wavelength of 60 μm, intersubband population inversion is achievable at acceptable injection current densities even for room‐temperature operation. However, achievement of intersubband population inversion is significantly more difficult at the shorter wavelength. The temperature and carrier transit time dependence of intersubband population inversion are also calculated.
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78.66.Fd III-V semiconductors
73.40.Gk Tunneling
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
42.55.Px Semiconductor lasers; laser diodes
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