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4 Mar 1991

Volume 58, Issue 9, pp. 879-987

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Effects of strained‐layer structures on the threshold current density of AlGaInP/GaInP visible lasers

Jun‐ichi Hashimoto, Tsukuru Katsuyama, Jiro Shinkai, Ichiro Yoshida, and Hideki Hayashi

Appl. Phys. Lett. 58, 879 (1991); http://dx.doi.org/10.1063/1.104492 (2 pages) | Cited 26 times

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We have investigated the effects of strained‐layer structures on the reduction of the threshold current density of AlGaInP/GaInP visible laser diodes. It was found that a remarkable reduction of the threshold current density could be realized by incorporating strained single quantum well structures in their active regions. The minimum threshold current density at room temperature under pulsed conditions is 215 A/cm2, which is by far the lowest value ever reported for AlGaInP/GaInP visible lasers and comparable to those of AlGaAs/GaAs lasers.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Dependence of lasing characteristics of quantum well lasers on substrate orientation: Tight‐binding theory

T. Takahashi, J. N. Schulman, and Y. Arakawa

Appl. Phys. Lett. 58, 881 (1991); http://dx.doi.org/10.1063/1.104466 (3 pages) | Cited 2 times

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Band‐structure analysis using the tight‐binding method indicates that there is a significant dependence of lasing properties of GaAs/AlGaAs quantum well lasers on substrate orientation, which suggests the importance of choosing the substrate orientation carefully for improving lasing properties. These results are mainly due to changes in the in‐plane effective mass of the heavy hole.
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42.55.Ah General laser theory
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
42.55.Px Semiconductor lasers; laser diodes
78.45.+h Stimulated emission

Channel waveguides in electro‐optic polymers using a photopolymer cladding technique

Paul R. Ashley and Thomas A. Tumolillo

Appl. Phys. Lett. 58, 884 (1991); http://dx.doi.org/10.1063/1.105210 (3 pages) | Cited 5 times

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Reported here is a new fabrication technique for forming channel waveguides in organic electro‐optic (EO) polymer materials. The process uses projection printing to directly expose inverted ridge channel patterns in a UV curing optical epoxy cladding layer. This technique is noncontact, requires no post processing, minimizes wall roughness, and can be used with any spin coatable EO polymer. Single‐mode channel waveguides have been demonstrated and characterized as well as phase modulator devices.
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42.79.Gn Optical waveguides and couplers
42.82.-m Integrated optics
78.20.Jq Electro-optical effects

Optical switching in a resonant tunneling structure

P. England, J. E. Golub, L. T. Florez, and J. P. Harbison

Appl. Phys. Lett. 58, 887 (1991); http://dx.doi.org/10.1063/1.104467 (3 pages) | Cited 19 times

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We describe the interaction of light pulses with a GaAs/AlAs resonant tunneling structure. We demonstrate that light with an average power of less than 10 μW can induce switching, and show that switching is accompanied by a change in the optical absorption. These results suggest a number of new applications for the resonant tunneling structure, including light‐by‐light switching.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
73.40.Gk Tunneling
42.79.Hp Optical processors, correlators, and modulators
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks

Coherent beams from high efficiency two‐dimensional surface‐emitting semiconductor laser arrays

P. L. Gourley, M. E. Warren, G. R. Hadley, G. A. Vawter, T. M. Brennan, and B. E. Hammons

Appl. Phys. Lett. 58, 890 (1991); http://dx.doi.org/10.1063/1.104468 (3 pages) | Cited 42 times

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We have fabricated and operated large two‐dimensional (2D) arrays of phase‐locked surface‐emitting semiconductor lasers. The arrays were fabricated by reactive ion beam etching of epitaxial Fabry–Perot resonators comprising GaAs/AlGaAs quantum wells surrounded by AlAs‐AlGaAs quarter‐wave mirrors. Different arrays corresponding to different pixel size (2–5 μm) and spacing (1–2 μm) were produced to investigate evanescent coupling between pixels. The arrays were photopumped so that the array size could be conveniently varied from 1×1, 2×2,... up to 20×20. Except for the 1×1 which emits a circular pattern, all arrays exhibit a well‐defined four‐lobed far‐field pattern in agreement with our theoretical analysis of the optical modes which predicts domination by the 2D out‐of‐phase eigenmode. As a consequence this pattern can be understood with simple Fraunhofer diffraction theory. The angular spread of the lobes, determined by the periodicity of the array elements, is 10° for the array with element size/spacing of 4/1 μm. The widths of the lobes are 6.7° for the 2×2 and narrow to 3.2° with increasing number of pixels in the array. The array exhibits a sharp onset for lasing, operation on a single longitudinal mode, and a linewidth which narrows to ∼1 Å with increasing array size. The differential power efficiency is as high as 70%. These observations provide further impetus and guidance for the development of 2D laser diode arrays.
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42.60.Fc Modulation, tuning, and mode locking
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.55.Px Semiconductor lasers; laser diodes

Quantitative evaluation of elastic properties of LiTaO3 crystals by line‐focus‐beam acoustic microscopy

J. Kushibiki, H. Takahashi, T. Kobayashi, and N. Chubachi

Appl. Phys. Lett. 58, 893 (1991); http://dx.doi.org/10.1063/1.105217 (3 pages) | Cited 13 times

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The line‐focus‐beam acoustic microscope system is applied to investigate the elastic properties of LiTaO3. Elastic inhomogeneities are detected quantitatively as a significant variation of leaky surface acoustic wave (LSAW) velocities in X‐112.2°Y LiTaO3 wafers. Large changes, about 2.5%, in LSAW velocities are observed in some wafers, which correspond to a difference between the velocities for single and multidomains. One of the causes is found to be in the poling process during wafer fabrication.
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43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography
62.65.+k Acoustical properties of solids
62.20.D- Elasticity
43.35.Pt Surface waves in solids and liquids

Low radio frequency biased electron cyclotron resonance plasma etching

Seiji Samukawa, Tomohiko Toyosato, and Etsuo Wani

Appl. Phys. Lett. 58, 896 (1991); http://dx.doi.org/10.1063/1.104469 (3 pages) | Cited 5 times

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A radio frequency (rf) biased electron cyclotron resonance (ECR) plasma etching technology has been developed to realize an efficient ion acceleration in high density and uniform ECR plasma for accurate Al‐Si‐Cu alloy film etching. In this technology, the substrate is located at the ECR position (875 G position) and the etching is carried out with a 400 kHz rf bias power. This Al‐Si‐Cu etching technology achieves a high etching rate (more than 5000 A/min), excellent etching uniformity (within ±5%), highly anisotropic etching, and Cu residue‐free etching in only Cl2 gas plasma. These etching characteristics are accomplished by the combination of the dense and uniform ECR plasma generation at the ECR position with the efficient accelerated ion flux at the ECR position by using 400 kHz rf bias.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
52.75.-d Plasma devices

Sideband development in a high‐power traveling‐wave tube microwave amplifier

D. Shiffler, J. D. Ivers, G. S. Kerslick, J. A. Nation, and L. Schachter

Appl. Phys. Lett. 58, 899 (1991); http://dx.doi.org/10.1063/1.104470 (3 pages) | Cited 11 times

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The work presented describes the characteristics of single stage and severed high‐efficiency, high‐power traveling‐wave tube amplifiers operating in X band at 8.76 GHz. Average amplified output powers of 210 MW have been achieved at 24% efficiency. At high output power levels (≳100 MW) sidebands develop increasing the average radiated power to over 400 MW with a microwave conversion efficiency of over 45%. In single frequency operation phase stability to within ±8° has been demonstrated.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
41.75.Ht Relativistic electron and positron beams

Possibility of a new phase transition in 7×7 structure on clean Si(111) surfaces

Akitoshi Ishizaka, Takahisa Doi, and Masakazu Ichikawa

Appl. Phys. Lett. 58, 902 (1991); http://dx.doi.org/10.1063/1.104471 (3 pages) | Cited 8 times

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Temperature dependences of reflection high‐energy electron diffraction intensities are measured for Si(111)‐7×7 clean surfaces. The temperature dependences of diffraction intensities for both 7×7 super spots and specular spots change above 830 K. These show the possibility of two states in the 7×7 structure. The high‐temperature phase of the 7×7 structure is stable up to 1090 K, following the well known phase transition between 7×7 and 1×1 structures.
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68.35.Rh Phase transitions and critical phenomena
64.70.K- Solid-solid transitions
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)

Thermal stability of PtSi contact to GexSi1−x

Q. Z. Hong, J. G. Zhu, C. B. Carter, and J. W. Mayer

Appl. Phys. Lett. 58, 905 (1991); http://dx.doi.org/10.1063/1.104472 (3 pages) | Cited 8 times

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Thermal stability of PtSi contact to epitaxial Ge0.5Si0.5/(100)Si has been investigated. The PtSi layer remained structurally and morphologically intact on the epitaxial Ge‐Si alloy at temperatures around 650 °C. When annealed at higher temperatures, PtSi penetrated locally into the alloy, although no chemical reaction was observed. The observed stability of PtSi is explained on the basis of a ternary Pt‐Ge‐Si equilibrium phase diagram. Other choices of contact compounds on Ge‐Si alloys are also discussed.
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68.35.Fx Diffusion; interface formation
68.55.Nq Composition and phase identification
68.35.Md Surface thermodynamics, surface energies

Preferential reaction and stability of the Au‐Sn/Pt system: Metallization structure for flip‐chip integration

Osamu Wada and Tsugio Kumai

Appl. Phys. Lett. 58, 908 (1991); http://dx.doi.org/10.1063/1.104473 (3 pages) | Cited 9 times

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Thermal reaction of a metallization system consisting of Au‐Sn solder, Pt/Ti barrier, and Au/Zn/Au contact layers formed on an InP substrate has been studied using Auger electron spectroscopy, scanning electron microscopy, and x‐ray diffractometry. Upon heating to 400 °C, no degradation of the Au/Zn/Au contact was noticed and moderate reaction was observed between Au‐Sn and Pt. The reaction shows a characteristic feature of preferential Pt‐Sn interdiffusion to produce an intermediate layer involving the PtSn phase. The effective diffusion coefficient exhibits an activation energy of 1.35 eV. The lifetime of this Pt barrier has been determined to be in excess of 108 h for 50 °C, being sufficient for the application of this metallization structure in practical device and flip‐chip integrated circuit fabrication.
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68.35.Fx Diffusion; interface formation
68.55.Nq Composition and phase identification
85.40.Hp Lithography, masks and pattern transfer
73.40.Jn Metal-to-metal contacts

Recombination properties of structurally well defined NiSi2 precipitates in silicon

M. Kittler, J. Lärz, W. Seifert, M. Seibt, and W. Schröter

Appl. Phys. Lett. 58, 911 (1991); http://dx.doi.org/10.1063/1.104474 (3 pages) | Cited 35 times

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We report first results on the recombination properties of structurally well defined NiSi2 precipitates in n‐type silicon. Under the conditions applied, precipitates form without the occurrence of punched out dislocations or any other secondary defects. We find that the minority‐carrier diffusion length (LD) measured by electron beam induced current (EBIC) is related to the precipitate density NV and LD ≂ 0.7 × NV−1/3. EBIC investigations of individual precipitates reveal contrasts up to 40% demonstrating NiSi2 particles to be efficient recombination centers.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.Nn Stacking faults and other planar or extended defects
81.40.Rs Electrical and magnetic properties related to treatment conditions

Infrared photoconductor fabricated with a molecular beam epitaxially grown CdTe/HgCdTe heterostructure

Shixin Yuan, Li He, Jinbi Yu, Meifang Yu, Yiming Qiao, and Jianmei Zhu

Appl. Phys. Lett. 58, 914 (1991); http://dx.doi.org/10.1063/1.104475 (3 pages) | Cited 12 times

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Infrared photoconductors fabricated with a CdTe/Hg0.64Cd0.36Te abrupt heterostructure grown on a GaAs substrate by molecular beam epitaxy are described here for the first time. The growth procedure, device fabrication, and measurement results are described. The results show that the devices have relatively high detectivity and uniformity. The observed enhancement in device performance attributed essentially to the large reduction in interface states and surface contamination by a subsequent growth of a lattice‐matched semi‐insulating CdTe epilayer for the passivation of HgCdTe surface.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ga II-VI semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Optical waveguide formed by cubic silicon carbide on sapphire substrates

Xiao Tang, Kobchat Wongchotigul, and Michael G. Spencer

Appl. Phys. Lett. 58, 917 (1991); http://dx.doi.org/10.1063/1.104476 (2 pages) | Cited 5 times

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Optical confinement in beta silicon carbide (β‐SiC) thin films on sapphire substrate is demonstrated. Measurements are performed on waveguides formed by the mechanical transfer of thin β‐SiC films to sapphire. Recent results of epitaxial films of SiC on sapphire substrates attest to the technological viability of optoelectronic devices made from silicon carbide. Far‐field mode patterns are shown. We believe this is the first step in validating a silicon carbide optoelectronic technology.
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85.60.-q Optoelectronic devices
78.66.-w Optical properties of specific thin films
78.30.-j Infrared and Raman spectra
78.40.Fy Semiconductors
78.20.Jq Electro-optical effects

Emission kinetic of the slow interface states in Si3N4/In0.53Ga0.47As structures

J. M. López‐Villegas, J. R. Morante, J. Samitier, A. Cornet, M. Renaud, and P. Boher

Appl. Phys. Lett. 58, 919 (1991); http://dx.doi.org/10.1063/1.104477 (3 pages) | Cited 2 times

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In this work we have studied the emission kinetics related to the slow interface states of metal Si3N4/In0.53Ga0.47As structures, by means of the analysis of isothermal transients measurements performed at constant capacitance. The transients show the presence of two kinds of slow interface states. One of them presents a kinetics which can be explained by means of a direct exchange of carriers with the semiconductor conduction‐band states. The other one shows a more complex emission kinetics. In this last case, the slow states emission is controlled by the occupancy factor of the fast interface states, and this suggests the existence of a connection mechanism between them.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.61.Ng Insulators
71.55.Eq III-V semiconductors
73.40.Gk Tunneling

Reduction of boron diffusion in silicon by 1 MeV 29Si+ irradiation

V. Raineri, R. J. Schreutelkamp, F. W. Saris, K. T. F. Janssen, and R. E. Kaim

Appl. Phys. Lett. 58, 922 (1991); http://dx.doi.org/10.1063/1.104478 (3 pages) | Cited 32 times

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Reduction of the transient diffusion of B, implanted in Si along [100] at 10 keV to a dose of 1×1013/cm2, after annealing at 900 °C for 10 s has been observed in samples irradiated with 1.0 MeV 29Si ions to a dose of 5×1013/cm2 or higher. A lower Si dose did not influence the transient B tail diffusion. Secondary defects formed near the peak of the 1 MeV Si damage distribution, for doses of 5×1013/cm2 and higher, act as efficient sinks for interstitials from shallower depths and thereby reduce the transient tail diffusion.
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61.80.Jh Ion radiation effects
66.30.Lw Diffusion of other defects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uf Ge and Si

Negative charge state of hydrogen species in n‐type GaAs

M. H. Yuan, L. P. Wang, S. X. Jin, J. J. Chen, and G. G. Qin

Appl. Phys. Lett. 58, 925 (1991); http://dx.doi.org/10.1063/1.104479 (3 pages) | Cited 21 times

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Having been exposed to hydrogen plasma, the Te‐doped GaAs wafers were deposited with metal Ti, to form the Ti/n‐GaAs Schottky barrier diodes (SBDs). The profiles of donor concentration after successive annealing of the hydrogenated SBD at several reverse biases at 100 °C, indicated that the donor concentration in the strong electrical field region of the depletion layer increase monotonically and the donor concentration in the weak electrical field region of the depletion layer decrease monotonically with time. It is confirmed that hydrogen can be present as a negatively charged species in n‐type GaAs and thus one can conclude that besides the deep donor level determined previously, hydrogen in GaAs has an acceptor level in the lower half of the energy gap or near the mid gap. There is evidence that the stronger the electrical field in strong field region of depletion layer, the faster the TeH complexes decompose in that region during a reverse bias annealing.
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71.55.Eq III-V semiconductors
61.72.U- Doping and impurity implantation
85.30.Hi Surface barrier, boundary, and point contact devices

Growth and structural characterization of embedded InAsSb on GaAs‐coated patterned silicon by molecular beam epitaxy

J. De Boeck, W. Dobbelaere, J. Vanhellemont, R. Mertens, and G. Borghs

Appl. Phys. Lett. 58, 928 (1991); http://dx.doi.org/10.1063/1.104480 (3 pages) | Cited 6 times

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The molecular beam epitaxial growth of InAsSb on GaAs‐coated patterned Si substrates is reported. The epilayers are grown embedded in wells so a coplanar Si‐InAsSb surface can be obtained. The InAsSb epilayer morphology is compared for different substrate conditions (Si−well, Si−mesa, GaAs) using Nomarski contrast microscopy. High‐voltage electron microscopy shows that the threading defect density of the InAsSb layers is high but decreases with thickness. In the reduced area electron diffraction pattern of the GaAs‐InAsSb interface, additional diffraction spots are visible due to microtwins in the InAsSb. High‐resolution electron microscopy reveals a regular array of misfit dislocations relieving the 14.2% lattice mismatch in the early stage of growth. Stripping Hall measurements for InAs0.05Sb0.95 show a constant mobility as a function of depth for the top 2 μm of the film and the 300 and 77 K mobility values are comparable.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
71.55.Eq III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Microwave detection of Shubnikov–de Haas oscillations in In0.53Ga0.47As/InP single quantum wells

P. Omling, B. Meyer, and P. Emanuelsson

Appl. Phys. Lett. 58, 931 (1991); http://dx.doi.org/10.1063/1.104481 (3 pages) | Cited 12 times

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Shubnikov–de Haas oscillations in 150 Å single quantum wells of In0.53Ga0.47As/InP are detected without contacts, using a conventional electron paramagnetic resonance (EPR) spectrometer. The two‐dimensional properties of the signal are verified and the carrier concentration is deduced from the period of the oscillations. The effective mass m∗ = 0.041mo obtained from the temperature dependence of the amplitude of the oscillations confirms that the signal originates from the In0.53Ga0.47As quantum well.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.61.Ey III-V semiconductors
78.70.Gq Microwave and radio-frequency interactions

Reduction of recombination centers in C‐doped p+‐GaAs/n‐AlGaAs heterojunctions by post‐growth annealing

Kazuo Watanabe, Hajime Yamazaki, and Kohji Yamada

Appl. Phys. Lett. 58, 934 (1991); http://dx.doi.org/10.1063/1.104482 (3 pages) | Cited 5 times

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The effect of post‐growth annealing at 500, 600, and 700 °C on the electrical characteristics of C‐doped p+‐GaAs/n‐AlGaAs junction diodes fabricated with metalorganic chemical vapor deposition layers has been investigated. Recombination current is reduced by post‐growth annealing at 600 and 700 °C, but not at 500 °C. The current reduction is primarily attributed to the dramatic reduction of 0.55 eV deep levels, which may be oxygen related complex levels. Under present annealing conditions, no degradation of carrier profiles near the p+‐n junction is detected. Thus, post‐growth annealing at temperatures of 600 °C or higher is a promising method for reducing recombination centers in the C‐doped p+‐GaAs/n‐AlGaAs junction.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Kk Junction diodes
71.55.Eq III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Linear optical properties of quantum wells composed of all‐binary InAs/GaAs short‐period strained‐layer superlattices

T. C. Hasenberg, D. S. McCallum, X. R. Huang, Martin D. Dawson, Thomas F. Boggess, and Arthur L. Smirl

Appl. Phys. Lett. 58, 937 (1991); http://dx.doi.org/10.1063/1.104483 (3 pages) | Cited 12 times

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The linear optical properties of a variety of (InAs/GaAs)‐GaAs multiple quantum well structures, where each well consists of a highly strained InAs/GaAs short‐period superlattice, have been investigated in detail. The results attest to the improvement in material quality over previously reported structures of this type. Clearly resolved excitonic absorption peaks have been observed at room temperature in all samples. Photoluminescence and excitonic absorption linewidths at 15 K are less than 10 meV in each case, with the photoluminescence Stokes shifted by less than 1 meV. Temporally resolved photoluminescence measurements at 15 K indicate carrier lifetimes of 1.4–1.8 ns. Dramatic strain‐related differences are observed when compared to random alloy InGaAs/GaAs quantum wells with an equivalent average indium mole fraction.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.55.Cr III-V semiconductors

Properties of metal/diamond interfaces and effects of oxygen adsorbed onto diamond surface

Yusuke Mori, Hiroshi Kawarada, and Akio Hiraki

Appl. Phys. Lett. 58, 940 (1991); http://dx.doi.org/10.1063/1.104484 (2 pages) | Cited 77 times

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The current‐voltage characteristics of Schottky diodes fabricated using as‐grown diamond films depend on the electronegativities of metals. However for diamond films oxidized by boiling in a saturated solution of CrO in H2SO4 or by exposure to an oxygen plasma, this dependence vanishes. This is because of the adsorption of oxygen onto the surfaces of diamond synthesized by chemical vapor deposition. It has been shown by x‐ray photoelectron spectroscopy that very little oxide is present on the as‐grown surfaces, but that at least submonolayer oxygen coverage is present on the oxidized surfaces.
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68.35.Fx Diffusion; interface formation
81.65.-b Surface treatments
85.30.Hi Surface barrier, boundary, and point contact devices

Simple approximation for Fermi energy in nonparabolic semiconductors

V. Altschul and E. Finkman

Appl. Phys. Lett. 58, 942 (1991); http://dx.doi.org/10.1063/1.104485 (3 pages) | Cited 13 times

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We propose a simple approximation relating the Fermi energy to carrier concentration in both parabolic and nonparabolic semiconductors. The solution is in the form of a polynomial correction to Boltzmann’s approximation of semiconductor statistics. The method is similar to the Joyce–Dixon series approximation, but uses polynomial regression to obtain series coefficients which extends the range of the model’s validity. For nonparabolic semiconductors, polynomial coefficients are calculated using Kane’s k☒p model for the density of states. The new approximation demonstrates an acceptable accuracy for band gaps larger than 2 kT and for the Fermi energy up to 10 kT. The expression is simple and should be useful in the modeling of advanced semiconductor devices.
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71.15.-m Methods of electronic structure calculations
72.80.Ey III-V and II-VI semiconductors
64.30.-t Equations of state of specific substances
85.30.De Semiconductor-device characterization, design, and modeling

Use of ultrathin oxides and thin polycrystalline silicon films for stable high‐efficiency silicon solar cells

P. E. Gruenbaum, J. Y. Gan, and R. M. Swanson

Appl. Phys. Lett. 58, 945 (1991); http://dx.doi.org/10.1063/1.104486 (3 pages) | Cited 5 times

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Initial designs of single‐crystal point‐contact solar cells showed a degradation in their efficiency due to photoinjected hot‐electron damage. We have examined the ultraviolet stability of ultrathin oxides covered by a thin polycrystalline silicon film and a thick oxide. Optical modeling has shown that these oxide/polycrystalline silicon/oxide stacks can have extremely good antireflection properties which offset the absorption losses from the polycrystalline silicon. Experiments have determined that these stacks are stable under ultraviolet exposure and that the polycrystalline silicon is absorbing less light than predicted. Point‐contact solar cells fabricated with this technique have achieved efficiencies as high as 24.4% under 36 W/cm2 of concentrated sunlight.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
84.60.Jt Photoelectric conversion
85.60.Dw Photodiodes; phototransistors; photoresistors
78.30.-j Infrared and Raman spectra
78.40.Fy Semiconductors

Differential photoreflectance from modulation‐doped heterojunctions

Michael Sydor, Ali Badakhshan, James R. Engholm, and Daniel A. Dale

Appl. Phys. Lett. 58, 948 (1991); http://dx.doi.org/10.1063/1.104487 (3 pages) | Cited 23 times

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We present a new photoreflectance (PR) technique for studies of layered electronic materials. Using the technique, we isolate the reflected signal from buried interfaces and extract the signature from the two‐dimensional electron gas in high electron mobility transistor. We compare the results from the technique with conventional PR measurements performed on sequentially etched samples. The results indicate that the new technique picks out the PR from buried interfaces and provides data on the in situ electric fields at the interfaces.
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85.30.Pq Bipolar transistors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
07.60.Hv Refractometers and reflectometers
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