The de-oxidation of a ZnTe surface by hydrogen treatment

Abstract

An oxide layer that covers MBE-ZnTe/GaAs has been removed by a very simple hydrogen (H₂) gas treatment. Intentionally oxidized ZnTe/GaAs samples were exposed to H₂ gas cracked using a tungsten heater located in a ceramic tube. The gas irradiation unit was inserted into the MBE growth chamber through a K-cell port. The diffused RHEED patterns of the oxidized ZnTe surfaces become spotty after exposure to cracked H₂ gas. H₂ treatment changes the half-width of the oxidized ZnTe X-ray rocking curve to correspond to the as-grown sample. After re-growth of ZnTe onto the treated ZnTe surface, the RHEED patterns changed from spotty to streaky. Elimination of the oxide layer on the ZnTe surface by this method requires a longer time than was the case for ZnSe.

Introduction

ZnTe attracts attention as it is a candidate for use as the missing green emitter in high-brightness LEDs [1], [2]. We usually grow ZnTe on GaAs or InP substrates by MBE. The lattice mismatch between ZnTe and GaAs is 7.7%, and that between ZnTe and InP is 3.9%. Even if we use InAs as the substrate, the mismatch is 0.76% and this is larger than the mismatch between ZnSe and GaAs. These substrates, however, result in opaque ZnTe-based devices in the visible region. Since ZnSe–ZnTe superlattices have a visible-light up-conversion effect [3] the fabrication of devices using transparent substrates will result in a drastic spread of application fields. The most suitable substrate for ZnTe is a ZnTe single crystal but surface preparation is difficult because the crystal is covered by an oxide layer. To fabricate a device using ZnTe a de-oxidation step is thus needed.

We have successfully cleaned the surface of MBE-ZnSe/GaAs using a convenient method. Samples were exposed only to cracked H₂ gas at the growth temperature in the MBE growth chamber [4]. The diffuse RHEED pattern of a ZnSe surface that had been oxidized artificially recovered within a few minutes the streaky pattern that characterized the de-oxidized surface. In this work, we apply this simple method to the ZnTe/GaAs. We expected the same effects for the ZnTe surface.