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27 Feb 1995

Volume 66, Issue 9, pp. 1027-1149

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Room‐temperature preparation of the highly crystallized luminescent CaWO4 film by an electrochemical method

Woo‐Seok Cho, Masatomo Yashima, Masato Kakihana, Akihiko Kudo, Tadayoshi Sakata, and Masahiro Yoshimura

Appl. Phys. Lett. 66, 1027 (1995); http://dx.doi.org/10.1063/1.113563 (3 pages) | Cited 49 times

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Highly crystallized polycrystalline film of single‐phase CaWO4 has been prepared on a tungsten substrate at room temperature in an alkaline solution containing calcium ions by an electrochemical method with the current density of 1 mA/cm2. This film showed blue emission (456 nm wavelength) with excitation light (254 nm wavelength) at room temperature. © 1995 American Institute of Physics.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
78.66.Li Other semiconductors
78.55.Hx Other solid inorganic materials

Double‐fused 1.52‐μm vertical‐cavity lasers

Dubravko I. Babić, James J. Dudley, Klaus Streubel, Richard P. Mirin, John E. Bowers, and Evelyn L. Hu

Appl. Phys. Lett. 66, 1030 (1995); http://dx.doi.org/10.1063/1.113564 (3 pages) | Cited 39 times

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We demonstrate a novel long‐wavelength vertical‐cavity laser structure employing two AlAs/GaAs mirrors and a strain‐compensated InGaAsP quantum‐well active region. The lasers have been fabricated by wafer fusion and have the lowest room‐temperature pulsed threshold current density of 3 kA/ cm2 at 1.52 μm. Eight laser sizes ranging from 9 to 60 μm were fabricated with threshold currents as low as 12 mA. Single transverse mode operation was observed on the 9 μm device, while other devices lased multimode. The maximum pulsed output power was 7 mW. © 1995 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation

Monolithic optical transmitter circuit using the InGaP/GaAs material system

D. T. Nichols, J. Lopata, W. S. Hobson, P. R. Smith, and N. K. Dutta

Appl. Phys. Lett. 66, 1033 (1995); http://dx.doi.org/10.1063/1.113565 (2 pages)

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A strained InGaP/GaAs/InGaAs multiquantum well laser has been monolithically integrated with GaAs metal–semiconductor field effect transistors (MESFETs) in a differential pair configuration to form a transmitter circuit. The structure utilized a single epitaxial growth step in which the laser was grown on top of the MESFET. The circuits operated with bandwidths as high as 4 GHz. © 1995 American Institute of Physics.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.82.Bq Design and performance testing of integrated-optical systems
42.55.Px Semiconductor lasers; laser diodes

Chemical bonding and atomic structure of Rb+ exchanged KTiOPO4 waveguides probed by micro‐Raman spectroscopy

David D. Tuschel, Gustavo R. Paz‐Pujalt, and William P. Risk

Appl. Phys. Lett. 66, 1035 (1995); http://dx.doi.org/10.1063/1.113566 (3 pages) | Cited 5 times

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Channel waveguides of Rb+ exchanged single‐crystal KTiOPO4 were studied by micro‐Raman spectroscopy. Rb+ exchange causes a disruption of the long‐range translational (crystal) symmetry of the lattice and a tilting of the TiO6 octahedra. The ability to nondestructively map the chemical and physical structure related to the optical properties of channel waveguides is demonstrated. © 1995 American Institute of Physics.  
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42.79.Gn Optical waveguides and couplers
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.30.Hv Other nonmetallic inorganics

Control of charge trapping in a photorefractive polymer

G. G. Malliaras, V. V. Krasnikov, H. J. Bolink, and G. Hadziioannou

Appl. Phys. Lett. 66, 1038 (1995); http://dx.doi.org/10.1063/1.114230 (3 pages) | Cited 22 times

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Modification of the trap density of the photorefractive polymer composite poly(N-vinylcarbazole) (PVK), 2,4,7-trinitro-9-fluorenone (TNF) and N,N-diethyl-para-nitroaniline (EPNA) was achieved with the addition of 4-(diethylamino)benzaldehyde diphenylhydrazone (DEH). Measurements of the response time, the phase shift and the amplitude of the photorefractive grating are presented. © 1995 American Institute of Physics.
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42.70.Jk Polymers and organics
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
72.40.+w Photoconduction and photovoltaic effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

High yield, low cost Fabry–Pérot modulators utilizing correctable partial antireflection coatings

K. W. Goossen, J. E. Cunningham, W. Y. Jan, and J. Centanni

Appl. Phys. Lett. 66, 1041 (1995); http://dx.doi.org/10.1063/1.113567 (3 pages) | Cited 5 times

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Reduced‐finesse asymmetric Fabry–Pérot modulators are presented utilizing partial antireflection coatings (PAR‐ASFP). Nonuniformity in semiconductor layer thicknesses may be corrected for by adjusting the thickness of the partial antireflection layer. Reduced thickness of the semiconductor layers is corrected for by reducing the thickness of the PAR layer, leading to natural extensions to manufacturing. By correcting the PAR, we obtain greater than 6.7:1 contrast over an entire 2 in. wafer at a single wavelength and drive voltage of 9 V. © 1995 American Institute of Physics.  
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42.79.Hp Optical processors, correlators, and modulators
78.66.Fd III-V semiconductors

Intrinsic multiple quantum well spatial light modulators

W. S. Rabinovich, S. R. Bowman, D. S. Katzer, and C. S. Kyono

Appl. Phys. Lett. 66, 1044 (1995); http://dx.doi.org/10.1063/1.113568 (3 pages) | Cited 26 times

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Large improvements are reported in the sensitivity of optically addressed multiple quantum well spatial light modulators. In prior work with these materials the quantum well region has been made semi‐insulating. It is shown that this is unnecessary and in fact detrimental to performance. By placing layers containing high trap concentrations at the ends of the structure and leaving the active quantum well layers intrinsic the speed of the device at a given illumination is improved by more than four times, diffraction efficiency is enhanced and spatial resolution is almost the same. © 1995 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
78.66.Fd III-V semiconductors

High reflectivity self‐pumped phase conjugation in an unusually cut Fe‐doped KTa1−xNbxO3 crystal

Xiaodong Mu, Zongshu Shao, Xuefeng Yue, Jun Chen, Qingcai Guan, and Jiyang Wang

Appl. Phys. Lett. 66, 1047 (1995); http://dx.doi.org/10.1063/1.113569 (3 pages) | Cited 3 times

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In this letter, a new type of self‐pumped phase conjugation (SPPC) is demonstrated and a phase conjugate reflectivity as high as 83.8% is measured in an unusually cut Fe‐doped KTa1−xNbxO3 (KTN:Fe) crystal with a He‐Ne laser. Some novel characteristics of this type of device are found, which may reduce the need for special crystal qualities to obtain SPPC. Finally, a possible mechanism is postulated to reasonably explain this type of SPPC. © 1995 American Institute of Physics.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Novel second‐order nonlinear optical, aromatic, and aliphatic polyimides exhibiting high‐temperature stability

Dong Yu, Ali Gharavi, and Luping Yu

Appl. Phys. Lett. 66, 1050 (1995); http://dx.doi.org/10.1063/1.113570 (3 pages) | Cited 10 times

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Novel aromatic and aliphatic polyimides exhibiting sizable second‐order nonlinear optical properties and long term thermal and temporal stability were synthesized. Detailed physical characterization revealed that the polymers are stable up to 300 °C with high glass transition temperatures (≳200 °C). Exceptional thermal stabilities at elevated temperatures were observed even at 150 °C. © 1995 American Institute of Physics.
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42.70.Jk Polymers and organics
78.66.Qn Polymers; organic compounds
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

All‐fiber femtosecond pulse amplification circuit using chirped Bragg gratings

A. Galvanauskas, M. E. Fermann, D. Harter, K. Sugden, and I. Bennion

Appl. Phys. Lett. 66, 1053 (1995); http://dx.doi.org/10.1063/1.113571 (3 pages) | Cited 21 times

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In‐fiber chirped Bragg gratings are used as stretchers and compressors for distortionless amplification of femtosecond pulses in chirped pulse amplification system. It is shown that using opposite directions of pulse propagation the effects of higher order dispersion and grating irregularities can be eliminated and the original pulse shape and duration can be recovered. Using these gratings a compact all‐fiber system consisting of a mode‐locked fiber oscillator and an erbium‐doped fiber amplifier was built. 330 fs bandwidth‐limited pulses from a fiber oscillator were stretched to 30 ps, amplified and recompressed back to 408 fs. The maximum energy of the pulses after the amplifier was 6 nJ and was at the threshold of nonlinear effects for a 30 ps stretched pulse. © 1995 American Institute of Physics.
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42.55.Wd Fiber lasers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.81.Wg Other fiber-optical devices

Laser cavity mirror imperfections and reflectivity: A time‐dependent numerical approach

Igor Vurgaftman and Jasprit Singh

Appl. Phys. Lett. 66, 1056 (1995); http://dx.doi.org/10.1063/1.113572 (3 pages) | Cited 1 time

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While the cleaving process used for semiconductor Fabry–Pérot lasers produces atomically abrupt mirrors, there is considerable interest in mirrors defined by etching. Depending on the etching process employed, disorder of varying nature and degree results at the semiconductor–air interface. A theoretical approach capable of quantifying the impact of such disorder on the mirror reflectivity, to which laser performance is intimately connected, is presented. The theoretical technique is time‐dependent to facilitate visualization of the scattering process and is based on a locally one‐dimensional implicit‐finite‐difference approximation to the two‐dimensional scalar wave equation with variable coefficients. Mirror disorder is described in terms of a feature depth parameter and an in‐plane correlation length. The reflectivity falls off exponentially with disorder yet is found to remain close to its unperturbed value for the disorder scale attainable with the state‐of‐the‐art etching technology. © 1995 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
81.65.-b Surface treatments

Measurements of sheath electric fields in a high pressure helium radio frequency discharge

M. D. Bowden, Y. W. Choi, K. Muraoka, and M. Maeda

Appl. Phys. Lett. 66, 1059 (1995); http://dx.doi.org/10.1063/1.113573 (3 pages) | Cited 16 times

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The importance of capacitively coupled radio frequency (rf) discharges has resulted in many attempts, by experiment and by simulation, to understand the dynamics of the discharge. Because of the time varying nature of the sheath potential, the sheath region is of special interest in these plasmas. Direct measurements are reported of the sheath electric fields in a helium plasma obtained using a laser induced fluorescence method. In the interpretation of these measurements, the time dependence of the fluorescence spectrum had to be considered. The measured electric field distributions can be used to deduce sheath widths. © 1995 American Institute of Physics.
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
52.80.Pi High-frequency and RF discharges
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Hydrogen passivation in nitrogen and chlorine‐doped ZnSe films grown by gas source molecular beam epitaxy

E. Ho, P. A. Fisher, J. L. House, G. S. Petrich, L. A. Kolodziejski, J. Walker, and N. M. Johnson

Appl. Phys. Lett. 66, 1062 (1995); http://dx.doi.org/10.1063/1.113574 (3 pages) | Cited 18 times

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The incorporation of hydrogen in ZnSe:N and ZnSe:Cl films grown by gas source molecular beam epitaxy (GSMBE) using elemental Zn and H2Se as source material has been investigated. The hydrogenation behavior was found to be significantly enhanced when nitrogen was used as a dopant, and typically resulted in highly resistive films. On the other hand, Cl‐doped ZnSe films showed a hydrogen concentration at or near the background levels independent of the Cl concentration. ZnSe was also grown by conventional molecular beam epitaxy with intentionally introduced H2 in order to clarify the source of the hydrogen. Significant hydrogen incorporation was observed in the MBE‐grown ZnSe:N layers only when hydrogen gas was introduced. Injection of hydrogen in excess of the amount generated during typical GSMBE experiments was found to give rise to an unambiguous increase in the hydrogen concentration, but with a hydrogen:nitrogen ratio less than that measured in GSMBE films. © 1995 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Greatly improved adhesion of gold films sputter-deposited on laser-treated and thermally annealed alumina

A. J. Pedraza, R. A. Kumar, and Douglas H. Lowndes

Appl. Phys. Lett. 66, 1065 (1995); http://dx.doi.org/10.1063/1.114231 (3 pages) | Cited 2 times

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The effects on adhesion strength of pulsed-laser irradiation prior to film deposition, and of thermal annealing following film deposition, have been studied for gold films deposited by ion beam sputtering on polished polycrystalline alumina (Al2O3) substrates. Three different atmospheres were employed for the laser irradiations: Ar-4% H2, air, and oxygen, all at 1 atmosphere pressure. A similar functional dependence of adhesion strength on laser energy density, Ed, was found for all of the gaseous environments: No change of adhesion strength for Ed ⩽ 0.5 J/cm2, maximum adhesion for Ed = 1.0–1.5 J/cm2, and decreased adhesion for higher Ed. A pronounced increase in gold-alumina adhesion strength was achieved when the alumina substrates were irradiated in an oxygen-rich atmosphere. A post-deposition 300 °C anneal doubled the adhesion strength to ∼50 MPa, approximately 500 times the strength of untreated gold-alumina couples. The adhesion strength initially increased rapidly with annealing time but saturated for times ⩾ 1 hour. The adhesion enhancement can be attributed to the formation of a high-energy disordered alumina surface during rapid solidification following pulsed-laser melting of the near-surface region. This defective surface contains reactive sites where gold atoms can form strong bonds. The data show that these sites most effectively bond gold atoms when they are saturated with oxygen. © 1995 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
68.35.Gy Mechanical properties; surface strains
81.15.Cd Deposition by sputtering
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Image widening not only a question of tip sample convolution

Jonas O. Tegenfeldt and Lars Montelius

Appl. Phys. Lett. 66, 1068 (1995); http://dx.doi.org/10.1063/1.113575 (3 pages) | Cited 5 times

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As the tip in the atomic force microscope is scanned over the sample surface an image results which contains information from the sample as well as from the tip. This mainly results in an increase of the apparent size of the sample. If the tip is reasonably sharp the contribution from the tip is small. In some cases the widening still persists in spite of a very sharp tip. In this letter, a model is presented which ascribes this to the lateral forces twisting the cantilever giving an offset between the apparent point of contact and the real point of contact. This results in a shift between forward and reverse scan of the sample position in the imaging window and, if the lateral forces due to the sample and substrate are different, a change in the apparent width of the sample. © 1995 American Institute of Physics.
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07.79.Lh Atomic force microscopes
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

In situ optical diagnosis on hydrogenated amorphous silicon grown by vibration superimposed plasma chemical vapor deposition

Nobuo Naito, Akihiro Takano, Masatomo Sumiya, Masashi Kawasaki, and Hideomi Koinuma

Appl. Phys. Lett. 66, 1071 (1995); http://dx.doi.org/10.1063/1.114284 (3 pages) | Cited 4 times

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p‐polarized 633 nm light reflection was in situ measured to detect a change, if any, in optical constants of hydrogenated amorphous silicon (a‐Si:H) thin films by the application of 2 MHz ultrasonic vibration to the substrate during their plasma chemical vapor deposition (CVD). Although the vibration scarcely changed the hydrogen content in a‐Si:H films under the reaction conditions of this study, it increased both the refractive index and absorption coefficient of a‐Si:H. The results are attributable to the densification of amorphous network structure as well as to the increase of density of extended states in the valence and conduction bands. Films with improved photoconductivity were obtained by the ultrasonic vibration assisted plasma CVD. © 1995 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.50.Pz Photoconduction and photovoltaic effects
71.55.Jv Disordered structures; amorphous and glassy solids

Electron effective masses in 4H SiC

N. T. Son, W. M. Chen, O. Kordina, A. O. Konstantinov, B. Monemar, E. Janzén, D. M. Hofman, D. Volm, M. Drechsler, and B. K. Meyer

Appl. Phys. Lett. 66, 1074 (1995); http://dx.doi.org/10.1063/1.113576 (3 pages) | Cited 45 times

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Results from optically detected cyclotron resonance (ODCR) studies of electron effective masses in 4H SiC are reported. ODCR measurements were performed on high‐purity n‐type 4H SiC epitaxial layers grown by chemical vapor deposition at both X band (9.23 GHz) and Q band (35.05 GHz) microwave frequencies. Electron effective masses in 4H SiC were directly determined as m⊥∗=0.42m0 and m∥∗=0.29m0. A scattering time in the basal plane τ⊥≊4.3×10−11 s, and hence, the corresponding electron mobility μ⊥≊1.8×105 cm2/V s, was obtained from a fit of the ODCR line shape. © 1995 American Institute of Physics.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
72.20.Fr Low-field transport and mobility; piezoresistance

Extremely high electron mobility in Si/SiGe modulation‐doped heterostructures

K. Ismail, M. Arafa, K. L. Saenger, J. O. Chu, and B. S. Meyerson

Appl. Phys. Lett. 66, 1077 (1995); http://dx.doi.org/10.1063/1.113577 (3 pages) | Cited 117 times

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We report record high electron mobility in modulation‐doped Si/SiGe. Samples grown by ultrahigh vacuum chemical vapor deposition (UHV‐CVD) with mobility values in the range of 3.2–5.2×105 cm2/V s have been measured at 0.4 K. The current and temperature dependence of the magnetoresistance in those samples have been examined and the scattering times are deduced from these measurements. At high magnetic field (≳10 T), fractional quantum Hall filling factors have been observed, and the corresponding activation energies have been calculated. These are significantly larger than previously reported values in Si/SiGe, and are comparable to those in GaAs/AlGaAs modulation‐doped heterostructures with mobility higher than 1×106 cm2/V s. © 1995 American Institute of Physics.
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73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Fq High-field and nonlinear effects
73.43.-f Quantum Hall effects

Investigation of the epitaxial growth of InxGa1−xAs on GaAs(001) and extension of two‐dimensional–three‐dimensional growth mode transition

Wei Li, Zhanguo Wang, Jiben Liang, Qiwei Liao, Bo Xu, Zhanping Zhu, and Bin Yang

Appl. Phys. Lett. 66, 1080 (1995); http://dx.doi.org/10.1063/1.113578 (3 pages) | Cited 5 times

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The growth of highly strained InxGa1−xAs (x≳0.25) epilayer on GaAs (001) undergoes a two‐dimensional–three‐dimensional (2D‐3D) growth mode transition beyond a critical thickness which depends on the strain. We show that the growth mode is controlled by the island‐edge diffusion carrier which originates from elastic energy relaxation at the edge of 2D island. The 2D‐3D growth mode transition depends upon whether or not a new layer nucleates on top of the island of 2 ML height before coalescence. The In atoms on the surface arising from surface segregation affect the island‐edge diffusion barrier and nucleation, leading to a 3D growth mode at the critical thickness. The experimental investigation is explained satisfactorily. © 1995 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Temperature activated conductance in GaN/AlGaN heterostructure field effect transistors operating at temperatures up to 300 °C

M. Asif Khan, Michael S. Shur, John N. Kuznia, Q. Chen, Jin Burm, and William Schaff

Appl. Phys. Lett. 66, 1083 (1995); http://dx.doi.org/10.1063/1.113579 (3 pages) | Cited 150 times

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We report on the dc characteristics and microwave performance of AlGaN/GaN heterostructure field effect transistors in the temperature range from 25 to 300 °C. At temperatures above 200 °C, we observe the temperature activated shunt conductance which is independent of the gate voltage (the activation energy is 0.505 eV). The cutoff frequency and the maximum frequency of oscillations vary from 22 and 70 GHz at 25 °C to 5 and 4 GHz at 300 °C, respectively. The gate leakage current in the range of gate biases from −4 to +1 V is small and nearly proportional to the gate voltage even at 300 °C. At temperatures above 200 °C, the gate leakage current is temperature activated (the activation energy is 0.88 eV). These results show that deep traps strongly affect the AlGaN/GaN characteristics at elevated temperatures. © 1995 American Institute of Physics.
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85.30.Tv Field effect devices
72.30.+q High-frequency effects; plasma effects

Epitaxial lift‐off of ZnSe based II–VI structures

C. Brys, F. Vermaerke, P. Demeester, P. Van Daele, K. Rakennus, A. Salokatve, P. Uusimaa, M. Pessa, A. L. Bradley, J. P. Doran, J. O’Gorman, and J. Hegarty

Appl. Phys. Lett. 66, 1086 (1995); http://dx.doi.org/10.1063/1.113580 (3 pages) | Cited 7 times

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The epitaxial lift‐off technique is applied to II–VI based structures. Epilayers of 255 nm thickness containing quantum wells are lifted off their substrates and redeposited onto polyimide coated GaAs. The technique has also been applied to II–VI samples onto which dielectric films had been deposited. Photoluminescence measurements show that the material quality has not been degraded during the processing. The success of this technique with II–VI’s opens up many possibilities for the integration of these materials with metals and dielectrics in vertical structure devices. © 1995 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.55.-a Thin film structure and morphology
85.40.Hp Lithography, masks and pattern transfer

Nonlinear optical response of hydrogenated amorphous silicon films studied by laser induced transient gratings

R. M. Ribeiro, W. Margulis, C. A. F. Leite, I. Guedes, L. Misoguti, and V. S. Bagnato

Appl. Phys. Lett. 66, 1089 (1995); http://dx.doi.org/10.1063/1.113581 (3 pages) | Cited 3 times

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The transient grating technique was used to study the optical properties of hydrogenated amorphous silicon films. A carrier lifetime τe=3.3 μs, a diffusion coefficient D=4.4×10−2 cm2/s, and effective third order nonlinear susceptibility χ(3)=(5.1±1.0)×10−7 esu were measured for λpump=532 nm. The electronic and thermal contributions of the grating were estimated by diffracting a continuous wave HeNe laser beam. For intensities 1.4–4.1 mW/cm2, ∼68% of the response at 633 nm is of electronic origin. A slowly rising diffraction component was also observed. © 1995 American Institute of Physics.
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42.65.An Optical susceptibility, hyperpolarizability
78.47.-p Spectroscopy of solid state dynamics
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
73.61.Jc Amorphous semiconductors; glasses

Optimization of interface parameters and bulk properties in ZnSe‐GaAs heterostructures

A. Bonanni, L. Vanzetti, L. Sorba, A. Franciosi, M. Lomascolo, P. Prete, and R. Cingolani

Appl. Phys. Lett. 66, 1092 (1995); http://dx.doi.org/10.1063/1.113582 (3 pages) | Cited 15 times

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The flux parameters employed during molecular beam epitaxy of ZnSe on GaAs control both the heterojunction band alignment and the optical quality of the II–VI wide‐gap layer. Independent optimization of the band discontinuities and ZnSe optical properties was achieved by fabricating a 2‐nm‐thick interface layer in nonstoichiometric conditions to control the band alignment, followed by the optically active layer in near‐stoichiometric conditions. © 1995 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Measurement of the electron ionization coefficient at low electric fields in InGaAs‐based heterojunction bipolar transistors

C. Canali, C. Forzan, A. Neviani, L. Vendrame, E. Zanoni, R. A. Hamm, R. J. Malik, F. Capasso, and S. Chandrasekhar

Appl. Phys. Lett. 66, 1095 (1995); http://dx.doi.org/10.1063/1.113583 (3 pages) | Cited 20 times

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The behavior of the electron impact‐ionization coefficient αn in In0.53Ga0.47As is measured with unprecedented sensitivity down to very low electric fields. The data are derived from measurements of the multiplication coefficient M−1 in suitably designed heterojunction bipolar transistors. Previously available data are extended by two orders of magnitude in the low field domain, down to αn≊1 cm−1. The experimental behavior of αn at fields below 200 kV/cm is in agreement with the theoretical prediction of a weak field dependence of αn at low electric fields. © 1995 American Institute of Physics.
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72.20.Ht High-field and nonlinear effects
72.80.Ey III-V and II-VI semiconductors

Transport study of self‐supporting porous silicon

A. Fejfar, I. Pelant, E. Šípek, J. Kočka, G. Juška, T. Matsumoto, and Y. Kanemitsu

Appl. Phys. Lett. 66, 1098 (1995); http://dx.doi.org/10.1063/1.113584 (3 pages) | Cited 18 times

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We have measured dark DC conductivity and time‐of‐flight (TOF) of carriers in self‐supporting porous silicon films in the temperature range 298–480 K. The dark I‐V curves show superlinear behavior with activation energies of 0.38–0.67 eV. The TOF measurements allowed us to evaluate the drift‐length of non‐equilibrium carriers and revealed a significant decrease of the collected charge with increasing delay (tdel≥1 ms) of the exciting 3 ns laser pulse after the voltage application, probably due to field redistribution in the Si crystallites. © 1995 American Institute of Physics.
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73.50.Pz Photoconduction and photovoltaic effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Le Other inorganic semiconductors
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