Photocapacitance and defect levels in gallium-doped zinc selenide

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Abstract
Although gallium in low concentration in ZnSe acts as a shallow donor, complex compensation effects occur if its concentration is increased, so the resistivity begins to increase with increasing impurity content. Slow wavelength scanning of the photocapacitance, infrared quenching of photocapacitance and transient photocapacitance have been used, therefore, to study the incidence of defect levels in Schottky diodes formed on ZnSe:Ga. All the devices exhibited an acceptor level 0.55 eV above the valence band, which is attributed to the self-activated acceptor complex (VZn-GaZn)'. With increasing gallium content the concentration of this acceptor appears to decrease, and a new shallower acceptor 0.40 eV above the valence band was observed in devices of ZnSe doped with 50 ppm gallium. For comparison, and as a control, the same photocapacitance techniques were used to place the copper acceptor 0.67 eV above the valence band.