I. Mojzes

Comparative mass spectrometric study of AIII-BV compounds covered with a gold layer

Abstract In situ mass spectrometric analysis of gaseous species evolved from gold coated GaP, InP, GaAs, InAs during heat treatment is described. The thickness of gold was 50 nm and 15 nm and a linear heating rate of 150°C min −1 was applied. The gold greatly enhanced the decomposition of compound semiconductors. During annealing the Au is saturated with the A III component, while the B V (volatile) component evaporates. On the evaporation vs temperature curves one or more peaks appear, depending on the thickness of gold layer and the type of compound semiconductor. The thicker the gold layer, the higher the volatile component loss and the higher the temperature of peak arsenic or phosphorus evolution.

Metal film barriers against the evaporation of volatile components during the heat treatment of metal-compound semiconductor contacts☆

Abstract InP samples covered with gold, Cr/Au, Ti/Au, Pd/Au, Pt/Au and Ni/Au metal films were heat treated in vacuum, and the evaporation of volatile components was monitored in situ with a mass spectrometer. In the case of Au-In samples, the interaction of gold with InP results in a large evaporation of the volatile component. It was found that chromium and titanium act as an effective barrier against this interaction. Nickel and platinum do not give rise to volatile component loss peaks but they are not effective barrier films to hinder the diffusion of gold. However, palladium promotes the decomposition of InP. This means that chromium and titanium should be preferred in contact systems as barrier metal films.

Effect of ion beam treatment on thermal annealing of GaAs-Au layer structures

Comparison of thermal annealing and ion mixing + thermal annealing on (100) GaAs-Au evaporated layers was made. The structures were investigated by SEM, X-ray diffraction, RBS + channeling and AES. Phase formation is retarded by ion implantation both for Ar and Xe, interdiffusion, however, is enhanced for Xe. Phases, as β-phase and GaAu2, were detected. An anomalous interdiffusion was found after low-dose Xe mixing, as gold penetration was deeper for 400°C post-annealing than for 500°C. Current-voltage characteristics of the diodes show that implantation procedure brings them nearer to ohmic behavior. Electrical measurements also point to a decrease of the number of defects as the annealing temperature increases up to 475°C in contrast to thermal annealing only [1].

The interaction of gold thin films with InP

Abstract The basic component of the most popular contacts to InP is gold. The interaction of gold with InP begins at low temperatures and is accompanied by the strong evaporation of phosphorus. The evaporation vs temperature curve is characterized by a multiple peak structure of the phosphorus loss. The peak structure is due to the formation of AuIn alloys with growing In content at higher temperatures, the formation and decomposition of a AuP compound and the melting of the metallization. Several samples were quenched at characteristic points of the evaporation vs temperature curve for further investigations. Scanning electron microscopy and Auger electron spectroscopic depth profiling of these samples showed changing surface morphology and increasing In content in the gold film in samples which were quenched subsequently at higher temperatures.

Comparative reliability study of n+−n and n+−n−n+ Gunn diodes

Abstract Two types of Gunn diodes submitted to biased life test at elevated temperature (70°C) show a difference in burn-out percentage. Based on an 8.5 × 105 device h investigation it was concluded that deterioration of the metallisation is the main failure mechanism for both types of diodes, but the fraction failed of n+−n−n+ type diodes is significantly lower than that of n−n+ type diodes.

Thermal behaviour of Au/AIIIBV samples controlled with mass spectrometer

Abstract Au/GaAs, Au/GaP and Au/InP samples were annealed in vacuum using a 150°C /min heating rate. The evaporation of volatile components (As and P respectively) were monitored with a mass-spectrometer during the heating cycle. The samples were quenched from different temperatures, characterized by typical points of the evaporation vs temperature curve. In this paper the RBS spectra of the samples heat treated in this way, will be discussed. After the heat treatment significant change in the surface morphology was observed by scanning electron microscopy. Different grains and protrusions appeared which belong to different intermetallic phases formed as a result of the interaction. Using X-ray diffractometric measurements we found Au 2 Ga and s-AuGa phases in the Au/GaAs samples. The same phases were also identified in the Au/GaP system. In the case of Au/InP contacts the phase identification is very difficult. The formation of Au 3 In 2 phaase is indicates by the X-ray spectra of the heat-treated Au/InP samples.

Electrical and microstructure analysis of Ni/Ge/n-GaAs interface

Ni(27 nm)/Ge(23 nm) and Ni(10 nm)/Ge(40 nm) layers deposited onto n-type GaAs by electron beam evaporation were studied structurally and electrically. The samples were annealed for 20 min at different temperatures in flowing forming gas—H2:N2 (5%:95%)—in tube furnace. The current–voltage characteristics of the samples annealed at 600°C show ohmic character. The contact resistance was found to be a minimum of 5.1×10−5 Ω cm2 after annealing at 600°C. The alloying behaviour of the specimens were investigated by electron microscopy. The contacts show a mixed structure in the case of as-deposited samples. In the sample annealed at 550°C, there appeared deep pyramidal pits of 20–30 nm size. The structural characterization was carried out by cross-sectional transmission electron microscope (XTEM) equipped with energy dispersive system (EDS). The composition investigations showed that the pits contained of Ga, As, Ni and Ge. The upper layer of the metal was very thin and rich in Ga. The layer between the semiconductor and the upper layer was a Ni–Ge(Ga, As) mixed one.

An advanced MESFET burn-in method and equipment

Abstract An advanced method was developed for MESFET burn-in purposes, based on preserving the samples in different stages of the degradation process—due to thermal and electrical stress—for subsequent structural investigations. This was performed by the automatic termination of the electrical stress separately on any device before its complete destruction. The equipment used for this method will also be described.

Intermetallic compound formation of Ge-Ni and Ge-Al-Ni systems by furnace annealing and ion beam intermixing

Abstract Ge-Ni and Ge-Al-Ni systems are candidates as contact materials for GaAs. This paper offers some data about the effect of aluminium on the formation of intermetallic phases between Ge and Ni. The presence of aluminium caused a phase separation but did not prevent the reaction only a delay was observed and intermetallic compounds were always found with furnace annealing in nitrogen ambient. The phase formation depended upon the aluminium concentration in germanium. For example, 60 at.% of Al in Ge shifted the formation temperature to 600°C and NiAl and Ni5Ge3 phases were detected, in contrast to 30 at.% where this temperature was only 400°C and single Ni5Ge3 phase was obtained. In addition, the Ge-Ni phases were also produced by ion beam intermixing using Ar+ and Xe+ beams. The samples were subjected to RBS and X-ray diffraction to measure the composition and to identify the phase, respectively. An intercomparison between the compounds produced by these two techniques will be presented.