A novel approach for making ohmic contacts to p-type ZnSe has been introduced. This approach includes growth of p-ZnSe at low temperature by a variant of molecular beam epitaxy, then treating the surface with KOH solution, followed by deposition of a Te/Pd/Pt/Au metal layer and annealing at 200–250 °C for 5 min. As a result, a stable ohmic contact up to a current density of 2 kA cm−2 was obtained. Using this contact fabrication procedure, a ZnSe-based quantum-well laser was demonstrated in continuous wave mode of operation at room temperature. The formation of the ohmic contact is suggested to be due to the presence of oxygen on the ZnSe surface, the creation of TeO2 at the metal/ZnSe interface, and the diffusion of Pd into ZnSe.

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Using deep level transient spectroscopy and photocurrent measurements we have investigated Schottky contacts formed on p-isotype Zn(SSe)/GaAs heterostructures grown by molecular beam epitaxy on p-GaAs(100) substrates. A deep level located at 0.6 eV above the ZnSe valence band is observed in agreement with literature data for p-type ZnSe, and is used as a reference level for the understanding of photocurrent transitions in the 0.8–3.0 eV energy range. The threshold energies obtained on a series of Zn(SSe)/GaAs samples are explained in terms of absorption processes from the ZnSe and GaAs valence bands, and from the nitrogen acceptor level and a deep level of the ZnSe layers located at 0.1 and 0.6 eV above the valence band maximum, respectively. These absorption processes towards the ZnSe and GaAs conduction bands have been finally used to give the values of the conduction and valence band offsets at p-ZnSe/p-GaAs interface. Our experimental data gives ΔEc=0.25±0.03 eV and ΔEv=1.00±0.05 eV in agreement with literature data for Zn-rich interfaces.

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