Part III – March 1969 - Papers- Vapor-Phase Growth of Epitaxial Ga As1-x Sbx Alloys Using Arsine and Stibine

A technique previously used to prepare alloys of InAs1-xPx and GaAsl-x Px, miry: the gaseous hydrides arsine and phosphine, has been extended to grow single -crystalline GaAs 1-x Sb x by replacing the phos-phine with stibine. Procedures were developed for handling and storing stibine which now make this chemical useful for vapor phase growth. This represents the first time that this series of alloys has been grown from the vapor phase. Layers of P -type GaSb and GaSb-rich alloys have been grown with the carrier concentrations comparable to the lowest ever reported. In addition, a p-type alloy containing 4 pct GaSb exhibited a mobility of 400 sq cm per v-sec which is equivalent to the highest reported for GaAs. RECENTLY, interest has been shown in the preparation and properties of GaAs1-xSbx alloys, since it was predicted1 that for compositions in the range of 0.1 < x < 0.5, they might provide improved Gunn devices. However, preparation of these alloys presents fundamental difficulties. In the case of liquid phase growth, the large concentration difference between the liquidus and solidus in the phase diagram, at any given temperature, introduces constitutional supercooling problems. It is likely that, for this reason, virtually no description of the preparation of GaAs1-xSbx by this technique has been reported. In the case of vapor phase growth, problems are presented by the low vapor pressure of antimony, and the low melting point of GaSb and many of these alloys. In previous attempts1 at the vapor phase growth of these materials, using antimony pentachloride as the source of antimony vapor, alloy compositions were limited to those containing less than about 2 pct GaSb. This was in part due to the difficulty of avoiding condensation of antimony on introducing it to the growth zone. A growth technique has recently been described2 for the preparation of III-V compounds in which the hydrides of arsenic and phosphorous (AsH3 and pH3) are used as the source of the group V element. With this method, GaAs1-xPx and InAs1-xPx have been prepared2&apos;3 across both alloy series with very good electrical properties. Since the use of stibine (SbH3) affords the potential for effective introduction of antimony to the growth apparatus, in analogy with the other group V hydrides, this growth method has been explored for the preparation of GaAs1-xSbx alloys. In addition to GaSb, these alloys have now been prepared with values of x as high as 0.8. In the case of GaSb, undoped p-type layers were grown with carrier concentrations equivalent to the lowest reported in the literature. Thus it has been demonstrated that, with this growth technique, all of the alloys in this series can be prepared. EXPERIMENTAL PROCEDURE A) Growth Technique. The growth apparatus, shown schematically in Fig. 1, and procedure are virtually identical to that described2 for the growth of GaAs1-xPx alloys, with the exception that phosphine is replaced by stibine.* HCl is introduced over the gallium boat to *Purchased from Matheson Co., E. Rutherford,N+J. transport the gallium predominantly via its subchlo-ride to the reaction zone, where it reacts with arsenic and antimony on the substrate surface to form an alloy layer. The fundamental limiting factors to the growth of GaAs1-xSbx alloys from the vapor phase, especially GaSb-rich alloys, are the low melting point of GaSb (712°C) and the low vapor pressure of antimony at this temperature (<l mm). Thus, relatively low antimony pressures must be employed, which, however, imply low growth rates. To provide low antimony pressures, very dilute concentrations of arsine and stibine in a hydrogen carrier gas were used. Typical flow rates (referred to stp) were about 4 cm3 per min of HC1 (0.06 mole pct)+ from 0.1 to 1 cm3 per min of ASH, (0.002 to 0.02 mole pct), and from 1 to 10 cn13 per min of SbH3 (0.02 to 0.2 mole pct), with a total hydrogen carrier gas flow rate of about 6000 cm3 per min. Although no precise data on decomposition. kinetics exist, it is known4 that stibine decomposes extremely rapidly at elevated temperatures. However, the high linear velocities attendent with the high total flow rate (about 2000 cm per sec) delays cracking of the stibine until it reaches the reaction zone and prevents condensation of antimony in the system. To improve the growth rates of the GaSb-rich alloys, growth temperatures just below the alloy solidus are main-