An experimental study of the alloying characteristics of a composite thin-film structure which is often used as an ohmic contact to GaAs is presented. A AuGe layer of eutectic composition covered by a thin-film of Ni and deposited on n-type epitaxial GaAs is investigated in order to better understand the relationship between the alloying behavior and the electrical properties of the contact. The barrier energy ϕBn and the specific contact resistance of the Ni/AuGe/GaAs system is measured for a wide range of alloy temperatures and times. The metallurgical properties of the Ni/AuGe/GaAs system are obtained with Auger electron spectroscopy and scanning electron microscopy. Auger spectroscopy combined with in situ sputter etching is used to determine depth-composition profiles for all constituents of both as-deposited and alloyed Ni/AuGe/GaAs contacts. In samples heat-treated below the AuGe eutectic temperature, Ni is found to move rapidly through the intervening AuGe layer to collect at the GaAs interface, and the effective value of ϕBn rises to the value characteristic of Ni/GaAs Schottky diodes. For heat-treatment above the AuGe eutectic temperature, ohmic contact behavior is observed, and uniform alloyed contact surfaces are found to result from the presence of Ni at the GaAs interface. Ga outdiffusion and surface accumulation resulting from GaAs dissociation occurs for all alloy temperatures and times. The Ga outdiffusion appears to be characterized by a very low activation energy.

Metallurgical and electrical properties of alloyed Ni/AuGe films on n-type GaAs

The low‐temperature properties of the excitation‐dependent (moving) emissions in Mg‐, Be‐, Cd‐, and Zn‐implanted GaAs layers are investigated with respect to changes in temperature and excitation intensity. The substrates used were epitaxial layers, melt‐grown n‐type crystals, and Cr‐doped semi‐insulating crystals. Donor concentrations of the n‐type substrates were in the range 5×1013 to 2×1018 electrons cm−3. Models explaining a large energy shift are presented for both Cr‐doped and n‐type substrates. The moving emissions are classified into three different cases: (a) donor‐acceptor‐pair emission in relatively pure weakly compensated crystals; (b) donor‐acceptor‐pair emission in impure strongly compensated crystals; and (c) a radiation transition from the conduction‐band tails to the valence band. The donor‐acceptor‐pair emission in the impure compensated crystals shows the shift to lower energy with an increase of temperature in the temperature range 4–50 °K, while the donor‐acceptor‐pair emission in pu...

Excitation-dependent emission in Mg-, Be-, Cd-, and Zn-implanted GaAs

The electrical characteristics of ion implanted compound semiconductors

Publisher Summary This chapter examines the different aspects of ion implantation in semiconductors Ion implantation is a superior technique for producing new materials, which are very difficult or impossible to produce by chemical methods Ion implantation is the introduction of foreign atoms or lattice irregularities in the solid An important feature of the introduction of foreign atoms by ion implantation is that this method is applicable to all kinds of materials Depth profiles of the implanted ions can be calculated reasonably well by the Lindhard theory in the case of amorphous material Apart from the bombardment techniques, which can move the atom during the measurement, possible methods for detecting the existence of impurity atoms and their location consist of nuclear magnetic resonance and electron spin resonance measurements It is found that multivacancies rather than single vacancies are normally produced by ion implantation because of the high flux density and high total dose of the implanted ions In the case of single crystals, enhancement of the penetration was observed The radiation enhanced diffusion is assumed to result from the increase of radiation induced vacancies, the occurrence of the secondary channeling and interstitial migration

Ion Implantation in Semiconductors

The amphoteric nature of silicon in gallium arsenide is used to develop diffusion and electrical compensation mechanisms. The diffusion mechanism is based on the formation and diffusion of nearest‐neighbor donor‐acceptor pairs. General solutions are presented that predict abrupt diffusion fronts for a wide range of pairing conditions. Experiments support the application of this mechanism to Si diffusion in GaAs at high concentrations. A compensation mechanism for amphoteric dopants is developed as well. The compensation process is driven primarily by the free‐electron concentration. Nearly complete compensation is predicted for large dopant concentrations.

Diffusion and electrical properties of silicon‐doped gallium arsenide

Backscattering of MeV 4He ions has been used to analyze the Ga and As content in SiO2 and Si3N4 dielectric layers deposited on single‐crystal GaAs substrates. Changes in impurity concentrations and distributions are seen after isothermal annealing at both 750 and 800°C. Evidence for Ga outdiffusion is clear.

I. V. Mitchell

Papers

Outdiffusion through silicon oxide and silicon nitride layers on gallium arsenide