The difficulties in obtaining well defined electrically active layers by ion implantation in gallium arsenide, and other bindary compound semiconductors, as compared with silicon, are discussed. An examination from first principles, in terms of the chemistry of the defect solid state, points to several complications which follow immediately from the existence of two sub-lattices in these compounds, and it is shown that these effects may be responsible for many of the problems reported in the literature. The use of carefully matched dual implants is proposed as a technique which takes account of the special requirements of compound semiconductors, and should thus lead to improved results. The need for better characterization of the substrate material, and close control of annealing stages, in order to optimize the advantages of the technique, is also emphasized.

Ion implantation in compound semiconductors–an approach based on solid state theory

Publisher Summary It is noted that Gallium arsenide (GaAs) specimens are generally grown by various techniques such as LEC, Bridgman, VPE, MOVPE, LPE, and MBE. These specimens exhibit different properties in terms of energy levels within the band gap due to differences in defect levels, and trace impurities or impurity complexes. This chapter illustrates many defects and complexes that can be expected to exist in GaAs. It describes many energy levels obtained by deep-level transient spectroscopy (DLTS), and related methods for determining trap and recombination levels in GaAs. The energy levels produced by high-energy irradiation are also presented. Furthermore, the chapter discusses the effects of Cr in GaAs to produce semi-insulating GaAs along with the possible role of oxygen or other levels in the same context. The effects of Group I-VI impurities are also presented. The chapter concludes with the discussion of recombination and generation, minority-carrier lifetime, and diffusion-length effects.

Impurity and Defect Levels (Experimental) in Gallium Arsenide

Electrical, Rutherford backscattering and transmission electron microscopy measurements have been carried out on GaAs samples implanted with 150 keV, 1.10 15 zinc ions/cm 2 and furnace annealed in the temperature range from room temperature to 900°C. A correlation between three types of measurement technique was established and four distinct annealing stages have been identified. For perfect recrystallization and maximum electrical activation an annealing temperature of 900°C is required. The maximum peak hole concentration was in the range 1–2.10 19 holes/cm 3 .

Electrical, Rutherford backscattering and transmission electron microscopy studies of furnace annealed zinc implanted GaAs

The effect of implanting high energy tellurium ions into single crystal GaAs has been investigated by transmission electron microscopy Results from annealing experiments on specimens implanted at room temperature show that two anneal stages centred near 200 and 600° C occur, the actual anneal temperature being dose dependent Non-crystalline surface layers were formed after implanting doses in the range 5×1013 to 5×1015 ions cm−2 at room temperature However, implanting similar doses at 180° C caused no change in crystallinity Thus the low temperature anneal stage which is the epitaxial recrystallization of the non-crystalline material, does not occur for the higher implant temperature The high temperature anneal stage is associated with the annealing out of tiny defects such as twins and/or stacking faults leaving a single crystal containing only dislocation loops The anneal stages observed by electron microscopy correlate with changes in sheet resistivity and Rutherford backscattering measurements on similar material It is suggested that changes in dislocation loop size and density at high temperatures are coincident with the attainment of electrical activity

An examination of tellurium ion-implanted GaAs by transmission electron microscopy

Ion implantation is an extremely attractive method of selectively doping semiconductors, in part because the as-implanted distribution of impurities can be accurately predicted. However, electrical activation of implanted dopants generally requires high temperature annealing which allows these impurities to redistribute by various mechanisms. This paper reviews the role of defects in redistribution during the annealing of ion-implanted semiconductors. Some problems are inherent in the annealing process and are commonly observed in various materials. These include enhanced diffusion, gettering, and redistribution during recrystallization. Some problems are peculiar to compounds and include the effects of encapsulation, imbalances in crystal stoichiometry, and unequal recoil of host atoms of different masses. Dual implants and various implant temperatures have been employed in an effort to avoid some of these problems. Pulse annealing methods have also been investigated which reduce redistribution by considerably shortening the anneal time. However, problems associated with redistribution of dopants during annealing still limit the effectiveness of implantations in compound semiconductors.

The role of defects in the diffusion and activation of impurities in ion implanted semiconductors

The electrical behavior of zinc ions implanted into chromium-doped semiinsulating gallium arsenide was investigated by measurements of the sheet resistivity and Hall effect Room temperature implantations were performed using fluence values from 10 to the 12th to 10 to the 15th power/sq cm at 60 keV The samples were annealed for 30 minutes in a nitrogen atmosphere up to 800 C in steps of 200 C and the effect of this annealing on the Hall effect and sheet resistivity was studied at room temperature using the Van der Pauw technique The temperature dependence of sheet resistivity and mobility was measured from liquid nitrogen temperature to room temperature Finally, a measurement of the implanted profile was obtained using a layer removal technique combined with the Hall effect and sheet resistivity measurements

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J. R. Hauser

Papers

The electrical properties of 60 keV zinc ions implanted into semi-insulating gallium arsenide

Charge storage effects in mylar resulting from electron irradiation.

Indium-zinc implanted gallium arsenide diodes