The characteristics of Fe-doped semi-insulating layers, with overgrown Zn-doped p-type layers, were investigated by means of scanning electron microscopy, secondary ion mass spectrometry, capacitance-voltage, and current-voltage measurements. The resistivity which was deduced from the current-voltage characteristics was found to be strongly dependent upon the Zn dopant concentration. The secondary ion mass spectrometry depth profiles revealed the occurrence of Zn accumulation at the semi-insulating/p-type interface, and the peak concentration of Zn accumulation increased with doping level and overgrowth time of the p-type layers. The accumulation of Zn at the semi-insulating/p-type interface was related to a reduction in semi-insulating layer resistivity. The accumulation of Zn at the interface could be minimized by using a short growth time, together with low or medium doping of the p-type layers. Such growth conditions led to higher semi-insulating layer resistivity.

W.H.Cheng, H.Kuwamoto, A.Appelbaum, D.Renner, S.W.Zehr: Journal of Applied Physics, 1991, 69[4], 1862-5