Victor G. Weizer

The Influence of Interstitial Ga and Interfacial Au (sub 2)P (sub 3) on the Electrical and Metallurgical Behavior of Au-Contacted III-V Semiconductors

The introduction of a very small amount of Ga into Au contact metallization on InP is shown to have a significant effect on both the metallurgical and electrical behavior of that contact system. Ga atoms in the interstices of the Au lattice are shown to be effective in preventing the solid‐state reactions that normally take place between Au and InP during contact sintering. In addition to suppressing the metallurgical interaction, the presence of small amounts of Ga is shown to cause an order of magnitude reduction in the specific contact resistivity. Evidence is presented that the reactions of GaP and GaAs with Au contacts are also drastically affected by the presence of Ga. The sintering behavior of the Au‐GaP and the Au‐GaAs systems (as contrasted with that of the Au‐InP system) is explained as due to the presence of interstitial Ga in the contact metallization. Finally the large, two‐to‐three order of magnitude drop in the contact resistance that occurs in the Au‐InP system upon sintering at 400 °C is...

The kinetics of the Au‐InP interaction

An analysis of the reaction of Au and Au‐In alloys with InP has permitted the identification of the mechanisms occurring during the first two stages of the Au‐InP interaction. The first stage of the interaction, during which the Au is converted to a saturated Au(In) solution, is controlled by the vacancy‐generation rate at the free surface of the metallization. The activation energy for this process is the activation energy for Au self‐diffusion. Evidence is presented for the existence of large localized variations in this value due to surface related effects. At the completion of stage I stage II becomes active and continues until the metallization is converted to Au3 In. This process, proceeding via an interstitial interchange mechanism, is many orders of magnitude slower than stage I. The rate‐limiting step, with an activation energy of 2.8 eV, is shown to be the diffusion of In from the InP‐metal interface. The P atoms that are released when In enters the metallization during stage I leave the system ...

The interaction of gold with gallium arsenide

Gold and gold‐based alloys, commonly used as solar‐cell contact materials, are known to react readily with gallium arsenide. Experiments designed to identify the mechanisms involved in these GaAs‐metal interactions have yielded several interesting results. It is shown that the reaction of GaAs with gold takes place via a dissociative diffusion process. It is shown further that the GaAs‐metal reaction rate is controlled to a very great extent by the condition of the free surface of the contact metal, an interesting example of which is the previously unexplained increase in the reaction rate that has been observed for samples annealed in a vacuum environment as compared to those annealed in a gaseous ambient. A number of other hard‐to‐explain observations, such as the low‐temperature formation of voids in the gold lattice and crystallite growth on the gold surface, are also explained by invoking this mechanism.

The effect of metal surface passivation on the Au-InP interaction

The effect of SiO2 encapsulation on reaction rates in the Au‐InP system was studied. Scanning electron microscopy and x‐ray photoelectron spectroscopy were used to investigate surface and/or interface morphologies and in‐depth compositional profiles. It was found that the rate of dissolution of InP into Au and subsequent phase transformations are largely dependent on the condition of the free surface of the metalization. SiO2 capping of Au is reported for the first time to suppress the Au‐InP reaction rate. The Au‐InP interaction is shown to be quite similar to the Au‐GaAs interaction despite differences in the behavior of the group‐V elements.

The structural and electrical properties of low‐resistance Ni contacts to InP

We have investigated the electrical and metallurgical behavior of the Ni‐InP contact system. Specific contact resistivity (Rc) values in the low 10−7 Ω cm2 range are achieved with Ni‐only contacts on n‐InP (Si: 1.7×1018 cm−3) by sintering at 400 °C for several minutes. The post‐sinter contact metallization consists of three layers, arranged in the sequence: InP/Ni3P/Ni2P/In. Extended sintering (40 min) at 400 °C brings about a rise in Rc to the 10−4 Ω cm2 range. After extended sintering, the contact metallization is found to consist of only two layers, arranged in the sequence: InP/Ni2P/In. Based on the correlation between low Rc and the presence of Ni3P at the metal‐InP interface, it is suggested that the presence of Ni3P is the cause of the low Rc values. We show that the sintering schedule used to achieve low values of Rc is accompanied by substantial metal‐InP interdiffusion that results in severe device degradation. We show, finally, that it is possible to achieve low values of Rc without incurring t...

High-bandgap solar cells for near-sun missions

High bandgap solar cells are to be preferred for near-Sun, high operating-temperature environments, such as will be encountered by a Mercury orbiter or the Solar Probe mission. A GaInP solar cell is well suited for elevated temperature performance because it is available and has a bandgap high enough to produce reasonable performance at temperatures above 400 °C. The cell is currently commercially available as the top cell of a multi-junction solar cell. A cell contact metallization needs to be developed that can operate without degradation at high temperature.

InGaAs monolithic interconnected modules (MIMs)

A monolithic interconnected module (MIM) structure has been developed for thermophotovoltaic (TPV) applications. The MIM device consists of many individual InGaAs cells series-connected on a single semi-insulating InP substrate. An infrared (IR) back surface reflector (BSR), placed on the rear surface of the substrate, returns the unused portion of the TPV radiator output spectrum back to the radiator for recuperation, thereby providing for high system efficiencies. Also, the use of a BSR reduces the requirements imposed on a front surface interference filter and may lead to using only an anti-reflection coating. As a result, MIMs are exposed to the entire radiator output, and with increasing output power density. MIMs were fabricated with an active area of 0.9/spl times/1 cm, and with 15 cells monolithically connected in series. Both lattice-matched and lattice-mismatched InGaAs/InP devices were fabricated, with bandgaps of 0.74 and 0.55 eV, respectively. The 0.74 eV MIMs demonstrated an open-circuit voltage (Voc) of 6.16 V and a fill factor of 74.2% at a short-circuit current (Jsc) of 0.84 A/cm/sup 2/, under flashlamp testing. The 0.55 eV modules demonstrated a Voc of 4.85 V and a fill factor of 57.8% at a Jsc of 3.87 A/cm/sup 2/. The near IR reflectance (2-4 /spl mu/m) for both lattice-matched and lattice-mismatched structures was measured to be in the range of 80-85%. Latest electrical and optical performance results for these MIMs is presented.

Contact spreading and the Au3In-to-Au9In4 transition in the Au-InP system

An investigation is made of the third stage in the series of solid‐state reactions that occur between InP and its most commonly used contact material, Au. This reaction, which results in the transformation of the contacting metallization from the pink‐colored Au3In to the silver‐colored Au9In4, is shown to be controlled by an In‐Au exchange or kickout mechanism operating at the interface between the two phases. Contact spreading, a rapid lateral expansion of the contact metallization that can consume large quantities of InP during growth, is shown to be another manifestation of this final stage in the InP‐Au reaction. A detailed description of the mechanisms, including an investigation of the kinetics of the processes involved, is presented.

Electrical and Optical Performance Characteristics of 0.74-eV p/n InGaAs Monolithic Interconnected Modules

There has been a traditional trade-off in thermophotovoltaic (TPV) energy conversion development between system efficiency and power density. This trade-off originates from the use of front surface spectral controls such as selective emitters and various types of filters. A monolithic interconnected module (MIM) structure has been developed which allows for both high power densities and high system efficiencies. The MIM device consists of many individual indium gallium arsenide (InGaAs) cells series-connected on a single semi-insulating indium phosphide (InP) substrate. The MIM is exposed to the entire emitter output, thereby maximizing output power density. An infrared (IR) reflector placed on the rear surface of the substrate returns the unused portion of the emitter output spectrum back to the emitter for recycling, thereby providing for high system efficiencies. Initial MIM development has focused on a 1 cm2 device consisting of eight series interconnected cells. MIM devices, produced from 0.74 eV InG...

High-performance, lattice-mismatched InGaAs/InP monolithic interconnected modules (MIMs)

High performance, lattice-mismatched p/n InGaAs/InP monolithic interconnected module (MIM) structures were developed for thermophotovoltaic (TPV) applications. A MIM device consists of several individual InGaAs photovoltaic (PV) cells series-connected on a single semi-insulating (S.I.) InP substrate. Both interdigitated and conventional (i.e., non-interdigitated) MIMs were fabricated. The energy bandgap (Eg) for these devices was 0.60 eV. A compositionally step-graded InPAs buffer was used to accommodate a lattice mismatch of 1.1% between the active InGaAs cell structure and the InP substrate. 1×1-cm, 15-cell, 0.60-eV MIMs demonstrated an open-circuit voltage (Voc) of 5.2 V (347 mV per cell) and a fill factor of 68.6% at a short-circuit current density (Jsc) of 2.0 A/cm2, under flashlamp testing. The reverse saturation current density (Jo) was 1.6×10−6 A/cm2. Jo values as low as 4.1×10−7 A/cm2 were also observed with a conventional planar cell geometry.