T. H. Chiu

A model for the surface chemical kinetics of GaAs deposition by chemical‐beam epitaxy

Recently we have reported the measurement of reflection high‐energy electron diffraction intensity oscillations during chemical‐beam epitaxy of GaAs using triethylgallium (TEG) and As2 derived from an arsine cracker [Appl. Phys. Lett. 50, 19 (1987)]. In this study we observed a significant variation of the GaAs growth rate with substrate temperature at constant TEG flux. In addition, the variation of growth rate with incident flux at constant temperature was found to be nonlinear below approximately 500 °C and linear above 500 °C for incident fluxes yielding maximum growth rates between 0.2 and 1.8 monolayers/s. We have developed a model of the surface pyrolysis of triethylgallium which explains the qualitative behavior of the above data. The model assumes the existence of adsorbed triethyl, diethyl, and monoethyl gallium species as well as adsorbed ethyl radicals. As a starting point, the rate limiting step to epitaxial incorporation of atomic gallium is assumed to be cleavage of the second ethyl–gallium...

Design and operation of antiresonant Fabry–Perot saturable semiconductor absorbers for mode-locked solid-state lasers

The antiresonant Fabry–Perot saturable semiconductor absorber (A-FPSA) has been successfully used to passively mode lock many different solid-state lasers. The main advantage of the A-FPSA is that important operation parameters such as the saturation intensity, losses, and impulse response can be influenced by the material and the device parameters and can be adapted to the requirements of solid-state lasers. We present a detailed quantitative discussion of the operation parameters, derive simple design rules, and show that the contribution of the A-FPSA to the starting and the stabilization of mode locking is much larger than the effect of Kerr lensing in a mode-locked Nd:YAG laser.

Room‐temperature operation of hot‐electron transistors

We demonstrate the first room‐temperature operation of a double heterojunction unipolar hot‐electron transistor. Our test structure has a current gain greater than 10 and a measured current drive capability in excess of 1200 A cm−2. The device uses an indirect, wide‐band‐gap AlSb0.92As0.08 emitter and the transistor base is a 100‐A‐wide InAs layer.

Observations on intensity oscillations in reflection high‐energy electron diffraction during chemical beam epitaxy

We report the observation of reflection high‐energy diffraction (RHEED) intensity oscillations during the growth of GaAs using triethylgallium in chemical beam epitaxy (CBE). The oscillation period corresponds exactly to the time required for the growth of one monolayer. RHEED oscillation studies also suggest the absence of flux transients due to switching of gas flows, abrupt and complete initiation and termination of growth with submonolayer resolution, and that CBE is capable of thickness control with submonolayer precision when coupled with the use of in situ RHEED intensity monitoring technique. The temperature and flux dependence of growth rates are also studied using RHEED oscillations. Results indicate that CBE growth is predominantly via a two‐dimensional layer‐by‐layer mechanism.

Delta-doped ohmic contacts to n-GaAs

A new type of nonalloyed ohmic contact to GaAs is realized by molecular beam epitaxy. The ohmic characteristic of the metal‐semiconductor junction is obtained by placing a highly δ‐doped donor layer a few lattice constants away from the metal‐semiconductor interface of the contact and thus keeping the tunneling barrier extremely thin. The current‐voltage characteristic of the δ‐doped contacts is strictly linear. The measured contact resistance is in the 10−6 Ω cm2 range. Theoretical analysis of the tunneling current through the triangular barrier predicts contact resistances in the range 10−7–10−9 Ω cm2. In spite of the high doping concentration (≂1021 cm−3) the surface morphology of the sample shows no degradation.

Strained quantum wells for polarization-independent electrooptic waveguide switches

A polarization-independent quantum well waveguide switch is demonstrated. By altering the composition and hence the degree of built-in strain, the bandgap of In/sub 1-x/Ga/sub x/As/InP quantum wells is engineered to produce equal field-induced refractive-index change in TE and TM polarizations. At the same time, the enhanced electrooptic effects characteristic of unstrained quantum wells are maintained, such that the voltage-length product for switching is only 3 V-mm. >

Gallium‐ and arsenic‐induced oscillations of intensity of reflection high‐energy electron diffraction in the growth of (001) GaAs by chemical beam epitaxy

The observations of a damped intensity oscillation using reflection high‐energy electron diffraction during the growth of GaAs by chemical beam epitaxy using triethylgallium and arsine are reported. It is experimentally demonstrated that the As flux can be instantly shut off without any memory effect by measuring the Ga‐induced intensity variation and the subsequent As‐induced oscillations. The Ga deposition, free of any background As contamination, makes possible the direct determination of metal‐alkyl adsorption and pyrolysis efficiency on the hot substrate surface. At 530 °C a (4×6) diffraction pattern is observed when Ga is deposited alone. The appearance of this (4×6) reconstruction along with the associated intensity behavior indicates that the first monolayer of Ga grows two‐dimensionally. This can be understood qualitatively in terms of the simple kinematic model involving only surface roughness. These observations support a two‐dimensional growth mechanism in the growth process. Furthermore, the ...

Diffusion of atomic silicon in gallium arsenide

Silicon impurities with an initial Dirac‐delta‐function‐like distribution profile are diffused into GaAs using rapid thermal annealing. The diffusion of atomic Si is determined by a novel method of comparing experimental capacitance‐voltage profiles with a corresponding self‐consistent profile calculation. Capacitance‐voltage profiles broaden from 30 to 137 A upon rapid thermal annealing at 1000 °C for 5 s. The diffusion coefficient and the activation energy of atomic Si diffusion in GaAs are determined to be D0=4×10−4 cm2/s and Ea=2.45 eV, respectively. The diffusion coefficient is two orders of magnitude smaller as compared to Si‐pair diffusion in GaAs.

Cr‐doped GaAs/AlGaAs semi‐insulating multiple quantum well photorefractive devices

Semi‐insulating multiple quantum well photorefractive devices using GaAs/Al0.29Ga0.71As with an electric field applied perpendicular to the layers are demonstrated. Semi‐insulating behavior is obtained by doping with Cr(1016/cm3) during epitaxial growth of the material. Diffraction efficiencies as high as 3% with an applied voltage of 20 V and microsecond response times are obtained in a 2 μm thick device. These devices are of importance for implementation of fast and sensitive two‐dimensional optical information processing systems at wavelengths compatible with current diode lasers without the spatial‐bandwidth limitations of thick photorefractive materials.

High-speed joint-transform optical image correlator using GaAs/AlGaAs semi-insulating multiple quantum wells and diode lasers

We demonstrate a compact real-time optical image correlator using diode lasers and a semi-insulating GaAs/AlGaAs multiple-quantum-well (SI-MQW) device as the holographic element. With only 3 mW of power incident upon the SI-MQW device, the correlation is obtained in 1 μs and can be erased in as fast as 2 μs, which presents the possibility of a system capable of 3 × 105 correlations/s. We also show that images can be stored for a controllable length of time (2–25 μs), which presents possibilities for the use of the SI-MQW device as a data or image buffer memory.