We examine the growth modes of compound semiconductors grown by molecular beam epitaxy in lattice matched and strained layers. While in lattice matched layers it is possible to grow in the layer by layer mode by choosing proper growth conditions, in strained layers we find that for large strain, it is not possible to do so. This is due to the competition between surface strain energy which favors 3D growth and surface chemical energy which favors a layer by layer growth mode. The growth mode is shown to have significant effects on the nature of the dislocations generated beyond critical thickness.

The macroscopic stress of 1.3μm and 1.5μm wavelength GaInAsP-InP channeled substrate buried heterostructure lasers is related with device reliability. The radius of curvature, R, of the device is taken as a measure of its macroscopic stress and the change in dc threshold current, ΔIth, after an accelerated aging test is taken as a measure of device reliability, with high ΔIth, indicating decreased reliability. R or ΔIth was changed by altering the p-side contact width or the p-side Au bonding pad thickness. No correlation was found between R and ΔIth. For example, changing the p-contact width from 6 to 125μm resulted in a reduction of ΔIth by a factor of 2 – 10 among the wafers studied. However, the change in the active layer stress, as determined by R−1, was at most only 25%. Similarly, increasing the Au bonding pad thickness from 0.6 to 9.0μm increased the active layer stress by a factor of 2, but with little change in Alt. It is concluded that the macroscopic stress does not affect device reliability for the GaInAsP lasers.

We describe techniques of reliable metallization in InP-based systems for application to discrete and opto-electronic integrated circuits (OEIC's). Strong metallurgical interaction between Au and InP-based compounds can cause serious contact degradation in light emitting diodes (LED's). By analyzing this interaction in detail, an improved thin Au/Zn/Au p-contact technique has been developed. The results are compared with Pt/Ti contacts, and it has shown that both provide sufficient reliability under temperature and current stresses in LED's. We then describe a metallization technique for flip-chip bonding of opto-electronic devices on other semiconductor chips for OEIC applications. An acceptable reaction barrier effect of Pt in AuSn/Pt/Ti metallization structure has been demonstrated and this structure has been used for a high-reliability, flip-chip integrated GaInAs/InP PIN photodiode/GaAs amplifier receiver circuit. We also discuss requirements for metallization for future monolithic OEIC's by taking up an example of metal-semiconductor-metal photodiodes in InP-based systems.

Forward bias capacitance has been used to examine the Au/W/GaAs and Au/Pt/Ti/GaAs Schottky barriers present in power microwave MESFET devices to see if interface-state generation plays any role in the previously reported reverse bias barrier height aging process. If a constant carrier capture cross-section is assumed, forward bias capacitance has shown that for samples strongly susceptible to aging (i.e. the Au/W/GaAs samples in this study) interface-state generation is taking place during the aging process. The validity of the constant capture cross section assumption has been tested by examining the I–V properties. For those samples whose reverse I–V properties were not dominated by thermionic-field emission, similar increases in interface-state densities were evaluated from the I–V characteristics for the degraded samples.

The reliability of ohmic contacts to thin, heavily doped layers of GaAs is investigated. Pd/Ge/Au contacts to n-type GaAs display excellent electrical stability over extended periods of thermal stress. The contact resistance stays below 0.50Ω-mim during a 2500h, 280°C bake. Reactive ion beam assisted evaporation of Ti with N forms TiN which is introduced as a barrier layer in Pt/TiN/Ti/Au contacts to a thin p+ layer. The TiN layer allows greater process latitude in the sintering process and improves long term stability of the ohmic contact. The microstructure of the p-type contacts is examined with TEM and Auger profiling at different instances of the 2500h, 280°C bake and compared to the contact resistance measurements.

Several compositions of A1-Pt thin films have been co-evaporated on GaAs substrates to study the stability of the alloys at high-temperature anneals. The A1 concentration in the alloys ranges from 45 at.% to 70 at.%, and we show that the films meet thermal stability requirements imposed by GaAs selfaligning gate technology for compositions between AIPt and Al2Pt.

The importance of contacts to photovoltaic solar cells is often underrated mainly because the required values of specific contact resistance and metal resistivity are often thought to be relatively modest compared with those associated with very large scale integration (VLSI) applications. However, due to the adverse environmental conditions experienced by solar cells, and since many of the more efficient cells are economically advantageous only when operated under solar concentration, the requirements for solar cell contacts are sometimes more severe. For example, at one-sun operation, the upper limit in specific contact resistance is usually taken to be 10−2 Ω-cm2. However, at several hundred suns, this value should be reduced to less than 10−4 Ω-cm2. Additionally, since grid line fabrication often relies on economical plating processes, porosity and contamination issues can be expected to cause reliability and stability problems once the device is fabricated. It is shown that, in practice, these metal resistivity issues can be much more important than issues relating to specific contact resistance and that the problem is similar to that of providing stable, low resistance interconnects in VLSI. This paper is concerned with the design and fabrication of collector grids on the front of the solar cells and, although the discussion is fairly general, it will center on the particular material indium phosphide. This III-V material is currently of great importance for space application because of its resistance to the damaging radiation experienced in space.

We report on experiments that were performed to evaluate the temperature stability and long term reliability of non-alloyed Pd-Ge-Au ohmic contacts on N-type GaAs. Low resistance contacts (≈1×10−6 Ωcm2) were obtained for samples that were sintered in a conventional furnace or flash sintered in a graphite susceptor. Elevated temperature storage (≈4000 hours at 280°C) showed improved contact stability when compared to Ni-AuGe-Ni-Au control samples. Gateless MESFETs subjected to bias temperature stress measurements (Ids ≈300–350mA/mm, 2000–4000 hours at 200°C) showed no significant change in device current. This result is in contrast to devices with Ni-AuGe-Ni-Au ohmic contacts which exhibited a 6–27% decrease in current under the same test conditions. Failure analysis reveals significant electromigration and Au diffusion in the drain fingers of devices with Ni-AuGe-Ni-Au contacts. In contrast, devices with Pd-Ge-Au contacts show no elect romigration or Au diffusion in the GaAs.

Au(85nm)/Pd(55nm)/GaAs(100) samples were heat treated in the 325–425°C temperature range. The annealed samples have been investigated using Rutherford Backscattering Spectrometry, Auger Electron Spectroscopy and Transmission Electron Microscopy. The gold layer remained largely unreacted up to 300°C. Significant Pd diffusion into GaAs consuming a 50–60 nm thick layer of GaAs is evident in the case of sample annealed at 325°C and a slight Au diffusion is also noticeable. In the sample annealed at 350°C the spreading of palladium was very quick. A strong reaction took place between the GaAs and the metallization in the case of sample heat treated at 375°C. At this temperature we have identified the PdGa phase using electron diffraction.

We shall study the thermoelectric power under classically large magnetic field (TPM) in optoelectronic materials of quantum wells (QWs), quantum well wires (QWW's), quantum dots (QDs) and compare the same with the bulk specimens of optoelectronic materials by formulating the respective electron dispersion law. The TPM increases with decreasing electron concentration in an oscillatory manner in all the cases, taking n-Hg1−xCdxTe as an example. The TPM in QD is greatest and the least for quantum wells respectively. The thecoretical results are in agreement with the experimental observations as reported elsewhere.