Band-Alignment of ZnSe/ZnSSe Based Layer Structures for Light Emitting Devices, Determination by Photocurrent Measurements

ZnSe-GaAs heterostructures are heterovalent semiconductor heterostructures which are almost lattice-matched, and appear in most recently demonstrated blue and blue-green lasers. The large valence band offset present in this heterojunction also hinders holes injection from the III-V substrate into the II-VI active layer. Using photocurrent (PC) measurements we have investigated Schottky contacts formed on p-isotype ZnSe/GaAs, ZnSSe/ZnSe/GaAs, ZnSe/ZnSSe/GaAs heterostructures and MESA quantum well light emitting diodes (LED´s) grown by MBE on p-GaAs (100) substrates. Some of the threshold energies obtained by photocurrent on different samples are explained in terms of absorption phenomena. These absorption processes have been used to give the values of the conduction and valence band offsets. Our experimental data gives DeltaE_{v (ZnSe/GaAs)}ap(0.95 plusmn 0.05) eV and DeltaE _{v (ZnSe/ZnSSe)}ap(0.137 plusmn 0.003) eV, DeltaE_{v (ZnSSe/GaAs)}ap(1.12 plusmn 0.06) eV, and DeltaE_{v (ZnSSe/CdZnSe)}ap(0.194 plusmn 0.006) eV. Numerical calculations by solving the Schrodinger equation in the effective mass approximation, give that the peak at 2.4 eV, 2.53 eV and 2.61 eV are assigned to transition hh_irarre_n. The totality of these results is in agreement with published data. A models based on band alignment is proposed explain different experimental peaks observed in the PC spectra