Shallow acceptor levels in Cu-doped GaAs crystals

Abstract

Doping of GaAs crystals by Cu from the melt o r by diffusion causes the appearance of an acceptor level system. Two levels of this system were intensively studied:the "deep" level (0.1 to 0.2 eV) (1,2) and the shallow one (0.02 t o 0.03 eV) ( 2 , 3 ) .In these papers the shallow level was supposed to be a simple defect occurring when Si replaces As in the lattice of GaAs.The connection of this level with Si was confirmed by u s by simultaneous doping with Cu and Si and p-type conductivity which causes an increase of N a s compared with the samples doped only with Cu at any composition of the melt.at least twice 1 aThe connection of N with residual Si has been pointed out also in ( 3 , 5). Haw-1 a ever, from the results of (6, 7) it follows that the concentration of electrically active Si in donor state, Si[SiGa]/ [SiAs] -2 (8). So the concentration independence of this ratio on composition may be supposed for Si must not practically depend on composition and Ga' too.As' If N is supposed to be the acceptor state of Si with E = 0.024 eV (9), then it is difficult to understand the complicated behaviour of the N concentration a s a function of melt composition C, which was found by us earlier (Fig. 1) (2). This fact stimulated our additional investigations on the nature of the shallow acceptor level.As 1 a