O. Ueda

Direct evidence for self‐annihilation of antiphase domains in GaAs/Si heterostructures

The nature and behavior of antiphase boundaries in GaAs/Si heterostructures using GaP, GaP/GaAsP, and GaAsP/GaAs strained‐layer superlattices as intermediate layers have been studied by transmission electron microscopy. The antiphase domains are found to be very complicated three‐dimensional polygons consisting of several subboundaries in different orientations. Self‐annihilation of antiphase domains during crystal growth of GaAs on (001) 0.4° off or (001) 2° off Si substrates is directly observed for the first time through plan‐view and cross‐sectional observations. Based on these findings, a mechanism of annihilation of these domains is presented.

Ultrahigh f/sub T/ and f/sub max/ new self-alignment InP/InGaAs HBT's with a highly Be-doped base layer grown by ALE/MOCVD

We report on a new self-alignment (SA) process and microwave performance of ALE/MOCVD grown InP/InGaAs heterojunction bipolar transistors (HBTs) with a base doping concentration of 1/spl times/10/sup 2/0 cm/sup -3/. We obtained f/sub T/ of 161 GHz and f/sub max/ of 167 GHz with a 2/spl times/10 /spl mu/m emitter. These high values indicate the best performance of InP/InGaAs HBTs ever reported, in so far as we know. These values were attained by reducing the base resistance using ALE/MOCVD and base-collector capacitance using a new SA process. These results indicate the great potential of these devices for ultrahigh-speed application.<<ETX>>

TEM investigation of modulated structures and ordered structures in InAlAs crystals grown on (001) InP substrates by molecular beam epitaxy

Abstract InAlAs crystals grown on (001) InP substrates by molecular beam epitaxy have been structurally investigated for the first time by transmission electron microscopy. Modulated structures lying in two equivalent directions of 〈100〉 and 〈010〉 are found in crystals grown at 500–560°C. In the crystals grown at temperature below 500°C, anomalous diffraction contrast elongating in the 〈110〉 direction is present. Ordered strutures of CuPt-type are also found in these crystals. Only two of the four equivalent variants are observed in the (110) cross-section. The super-spots are observed only in the crystals grown at 435–505°C and their intensity is weaker than in MOCVD-grown InGaP. These results suggest that the ordering is not perfect and that ordered regions are likely to be microdomains.

Reliability issues in III–V compound semiconductor devices: optical devices and GaAs-based HBTs

Abstract This paper reviews the current status of reliability issues in III–V optical devices, semiconductor lasers and light emitting diodes, and GaAs-based heterojunction bipolar transistors (HBTs). First, material issues in III–V alloy semiconductors and our current understanding of degradation in III–V semiconductor lasers and light emitting diodes are systematically presented. Generation of defects and thermal instability are among these issues for these systems. Defects introduced during crystal growth are classified into two types: interface defects and bulk defects. Defects belonging to the former type are stacking faults, V-shaped dislocations, dislocation clusters, microtwins, inclusions, and misfit dislocations, and the latter group includes precipitates and dislocation loops. Defects in the substrate can also be propagated into the epi-layer. Structural imperfections due to thermal instability are also found. They are quasi-periodic modulated structures due to spinodal decomposition of the crystal either at the liquid–solid interface or growth surface, and atomic ordering which also occurs on the growth surface through migration and reconstruction of the deposited atoms. Three major degradation modes of optical devices, rapid degradation, gradual degradation, and catastrophic failure, are discussed. For rapid degradation, recombination-enhanced dislocation climb and glide are responsible for degradation. Differences in the ease with which these phenomena occur in different heterostructures are presented. Based on the results, dominant parameters involved in the phenomena are discussed. Gradual degradation takes place presumably due to recombination enhanced point defect reaction in GaAlAs/GaAs-based optical devices. This mode is also enhanced by the internal stress due to lattice mismatch. However, we do not observe this mode in InGaAsP/InP-based optical devices. Catastrophic failure is found to be due to catastrophic optical damage at a mirror or at a defect in GaAlAs/GaAs double-heterostructure (DH) lasers, but not in InGaAsP/InP DH lasers. In each degradation mode, the role of defects in the degradation and methods of elimination of degradation are discussed. Secondly, we review the current status of two major reliability issues in GaAs-based HBTs, particularly InGaP/GaAs HBTs: degradation in current gain (β) and variation of turn-on voltage (Vbe). In the case of AlGaAs/GaAs HBTs, the β gradually decreased, then drastically degraded. After degradation, the device exhibits an increase in base current Ib, which has an ideality factor n≈2 in the Gummel plot. The activation energy for the degradation was estimated to be 0.6 ± 0.1 eV. On the other hand, in InGaP/GaAs HBTs, much higher reliability than in AlGaAs/GaAs HBTs was achieved although the degradation mode is similar. The estimated Ea and time to failure for InGaP/GaAs HBTs are 2.0 ± 0.2 eV and 106 h at Tj = 200°C, respectively, which are the highest values ever reported. We also review previously proposed degradation mechanisms for GaAs-based HBTs: hydrogen reactivation, microtwin-like defect formation, dark defect formation and carbon precipitation. TEM observation of a degraded InGaP/GaAs HBT indicated that there are at least two possible degradation mechanisms: formation of carbon precipitates in the base region and migration of metallic impurities from the base electrode to the base region. The second issue is concerned with the exponential increase in Vbe with operating time. The mechanism for the increase in Vbe has been clarified based on reactivation of passivated carbon acceptors in the base region during operation. If the device suffers from H+ isolation, Vbe rapidly decreases at the initial stage, then exponentially increases. The first stage of Vbe variation can be explained by the fact that a high density of hydrogen atoms migrating from the isolation region to the intrinsic base region, passivate the carbon atoms at the initial stage. From these results, one can expect that the use of He+ as an implant instead of H+ can solve this problem.

Transmission electron microscopic observation of InGaP crystals grown on (001)GaAs substrates by metalorganic chemical vapor deposition

Abstract The detailed nature of ordered structures and the effect of rotation of the substrates on their formation are studied by transmission electron microscopy, for the first time, in InGaP crystals grown on (001)GaAs subtrates by atmospheric metalorganic chemical vapor deposition. In InGaP crystals grown with substrate rotation, ordering occurs in column III atoms on only one of the four equivalent (111) planes with doubling in periodicity of (111) layers, i.e. … In/Ga/In/Ga/In/Ga/…. The ordering of the crystals is not perfect, and the ordered regions are found to be plate-like micro-domains lying on nearly the (001) plane. On the other hand, without rotation of the substrate, ordering occurs on two equivalent (111) planes and the size of the ordered domains becomes larger with a drastic increase of relative volume of the ordered regions. Independent of substrate rotation, modulated structures are observed in two equivalent 〈100〉 directions.

Catastrophic degradation of InGaAsP/InGaP double‐heterostructure lasers grown on (001) GaAs substrates by liquid‐phase epitaxy

Catastrophically degraded InGaAsP/InGaP double‐heterostructure lasers grown on (001) GaAs substrates by liquid‐phase epitaxy, emitting at 727 and 810 nm are investigated by photoluminescence topography, scanning electron microscopy, transmission electron microscopy, and energy dispersive x‐ray spectroscopy. The degradation is mainly due to catastrophic optical damage at the facet, i.e., development of 〈110〉 dark‐line defects from the facet, and rarely due to catastrophic optical damage at some defects, i.e., development of 〈110〉 dark‐line defects from the defects inside the stripe region. These 〈110〉 dark‐line defects correspond to complicated dislocation networks connected with dark knots, and are quite similar to those observed in catastrophically degraded GaAlAs/GaAs double‐heterostructure lasers. The degradation characteristics of the InGaAsP/InGaP double‐heterostructure lasers are rather similar to those in GaAlAs/GaAs double‐heterostructure lasers concerning the catastrophic degradation.

Defect structure of degraded Ga1−xAlxAs double‐heterostructure light‐emitting diodes

The defect structure of degraded Ga1−xAlxAs double‐heterostructure (DH) light‐emitting diodes (LED’s) was investigated by electroluminescence (EL) topography and transmission electron microscopy (TEM). Two types of dark‐line defects (DLD’s), 〈100〉 DLD’s and 〈110〉 DLD’s, and dark‐spot defects (DSD’s) were observed in EL patterns of degraded LED’s. Dislocation dipoles or large zigzag‐shaped dislocation loops were associated with DSD’s and 〈100〉 DLD’s. The dipoles had Burgers vectors of the type (a/2) 〈011〉 inclined at 45° to the (001) junction plane or (a/2) 〈110〉 parallel to the junction plane and were extrinsic in character. The zigzag‐shaped dislocation loops had Burgers vectors of the type (a/2) 〈011〉 and were extrinsic in character. On the other hand, multiple stacking faults which lay in 〈110〉 directions or half dislocation loops which also lay in 〈110〉 directions and had Burgers vectors of the type (a/2) 〈011〉 inclined at 45° to the junction plane or (a/2) 〈110〉 parallel to the junction plane were as...

Transmission electron microscope observation of dark‐spot defects in InGaAsP/InP double‐heterostructure light‐emitting diodes aged at high temperature

Dark‐spot defects revealed in the electroluminescence patterns of degraded InGaAsP/InP double‐heterostructure light‐emitting diodes that are operated at the current density of 8.0 kA/cm2 at 200 °C were investigated using transmission electron microscopy. Bar‐shaped defects lying in the direction of 〈100〉 or 〈110〉 were observed corresponding to the dark defects. These defects were precipitates of a certain kind of metal or compound and not ’’dislocationlike’’ ones.

Nature of dark defects revealed in InGaAsP/InP double heterostructure light emitting diodes aged at room temperature

The nature of the dark defects which have appeared in the InGaAsP/InP double heterostructure light emitting diodes aged at room temperature were studied by transmission electron microscopy and other related methods. According to the observation of many diodes by electroluminescence topography, the dark defects were classified into five types: cross‐hatched 〈110〉 dark line defects, regular tetragonal 〈110〉 dark line defects, regularly distributed dark spot defects, dark band defects, and dark spot defects whose circumference was bright. These dark defects corresponded to misfit dislocations, stacking faults which originated from the interface between the epitaxial layer and the substrate, precipitate‐like spherical defects, mechanical damages induced during epitaxial growth, and alloyed regions produced by the penetration of the electrode metals, respectively. It was found that both the dislocation glide process and the dislocation climb motion due to the nonradiative recombination of the minority carriers...

Defect structures in rapidly degraded InGaAsP/InGaP double‐heterostructure lasers

Rapidly degraded InGaAsP/InGaP double‐heterostructure lasers grown on (001)‐oriented GaAs substrates by liquid phase epitaxy have been investigated by photoluminescence topography and transmission electron microscopy. 〈100〉‐dark‐line defects and 〈110〉‐dark‐line defects are observed in the degraded region. The 〈100〉‐dark‐line defects correspond to interstitial type dislocation dipoles caused by recombination enhanced dislocation climb. Their origins are threading dislocations, V‐shaped dislocations, and dislocation networks. The 〈110〉‐dark‐line defects correspond to faulted dipoles extended from small faulted loops in the active layer, edge dipoles extended from threading dislocations, and glide dislocations. The velocities of the 〈100〉‐dark‐line defects are estimated by the operating time and the length of the dark lines, and are quite similar to those in rapidly degraded GaAlAs double‐heterostructure lasers.