A deep centre with excited states in MOVPE GaP grown under high phosphorus pressure

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Abstract
Using junction-space-charge techniques, a deep centre with excited states has been studied in undoped MOVPE n-type GaP grown under high phosphorus pressure. The ground-state and excited-state energy positions have been determined to be 0.82 and 0.16 eV below the conduction-band edge respectively. The photoionisation cross section for electrons shows a pronounced photo-thermal excitation behaviour. The kinetic properties of electron excitation and recombination are analysed using a model for two-step excitation. A method for determining the thermal activation energy of the dominant excited state is described. Comparing the results with those published previously, a possible relation of the centre to Ni(d9) is discussed.