CARBON DOPING CHARACTERISTICS OF GAAS AND AL0.3GA0.7AS GROWN BY ATMOSPHERIC-PRESSURE METALORGANIC CHEMICAL-VAPOR-DEPOSITION USING CCL4

Abstract

This paper presents the results of a Van der Pauw-Hall analysis of the carbon doping characteristics of GaAs and Al0.3Ga0.7As epilayers grown by atmospheric pressure metalorganic chemical vapor deposition (AP-MOCVD) using carbon tetrachloride (CCl4). It also describes the effects of rapid thermal annealing (RTA) on the electrical properties of CCl4-doped GaAs. Heavily CCl4-doped GaAs and Al0.3Ga0.7As epilayers with a wide range of hole concentrations were obtained by varying the growth temperature from 500 to 750-degrees-C and by varying the V/III (AsH3/TMG) ratio from 5 to 20 while keeping the flow rate of CCl4 constant. CCl4-doped GaAs epilayers with hole concentrations between 3.5 x 10(17) and 8.95 x 10(19) cm-3 were obtained under the above growth conditions with constant TMG flow rate. CCl4-doped Al0.3Ga0.7As epilayers have higher hole concentrations than CCl4-doped GaAs epilayers for various growth temperatures at the same V/III ratio and CCl4 flow rate, and the hole concentration increases with decreasing growth temperature. The CCl4-doped GaAs epilayers have nearly the same Hall mobilities as GaAs C-doped by V/III ratio control, but higher mobilities than Zn-doped GaAs. Our results show that the free hole concentration in heavily CCl4-doped GaAs epilayers increases after RTA at 790-degrees-C. This can be attributed to the decrease in the concentration of the hydrogen atoms caused by the breaking of the C-H or C-H(x) bonds. After longer annealing at 790-degrees-C the hole concentration decreases and the hole mobility increases. It is suggested by the increase in free hole concentration by RTA that the activation efficiency of the incorporated carbon in the as-grown CCl4-doped GaAs epilayers is incomplete.