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Hole conductivity and compensation in epitaxial GaN:Mg layers

Löcherleitfähigkeit und Kompensation in GaN:Mg Epitaxieschichten
: Kaufmann, U.; Schlotter, P.; Obloh, H.; Köhler, K.; Maier, M.


Physical Review. B 62 (2000), Nr.16, S.10867-10872
ISSN: 0163-1829
ISSN: 1098-0121
ISSN: 0556-2805
Fraunhofer IAF ()
GaN:Mg; hole conductivity; Löcherleitung; compensation; Kompensation

The concentration p and the mobility mu of holes in metal-organic chemical vapor deposition (MOCVD) GaN:Mg layers were studied by room temperature Hall-effect measurements as a function of the Mg concentration N(A) in the range 3 x 10(exp 18) cm(exp-3) <= N(A) <= 1 x 10(exp 20) cm(exp -3). The hole density first increases with increasing N(A), reaches a maximum value p(max)~6*10(exp 17) cm(exp -3) at N(A)~2*10(exp 19) cm(exp - 3), decreases for larger N(A) values, and drops to very small values at N(A) 1 x 10(exp 20) cm(exp -3). The hole mobility decreases monotonically with increasing N(A) . The p(N(A)) data provide strong evidence for self-compensation, i.e., for a doping driven compensation of the Mg acceptor by intrinsic donor defects. This effect becomes significant when N(A) exceeds a value of 2 x 10(exp 19) cm(exp -3). A semiquantitative self-compensation model involving nitrogen vacancies is developed. It accounts satisfactorily for the measured p(N(A)) dependence and suggests that self-compensation limits the hole conductivity in bulklike MOCVD GaN:Mg layers grown near 1300 K to about 1.2 (omega cm)(exp -1)).