Explanation of Observed P-Type Conductivity in MOVPE ZnSe/GAAs Heterostructures
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EXPLANATION OF OBSERVED P-TYPE CONDUCTIVITY IN MOVPE ZNSE/GAAs HETEROSTRUCTURES O.BRIOT T. CLOITRE, N. TEMPIER, R. SAUVEZON, M. AVEROUS and R.L. AULOMBARD GES, USTL Place E. Bataillon, 34095 Montpellier Cedex 5 France, On leave from ASM France, Rte. de St.Geoges d'Orques, 34990 Juvignac France.
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ABSTRACT Together with the advanced growth technologies of zinc selenide epitaxial films by MOVPE or MBE, severals workers have reported the observation of p-type conductivity in this material. However, there are some inconsistencies in most of the papers reporting such results. We report here the MOVPE crystal growth of nominaly undoped ZnSe/GaAs S.I. layers using alkyls as precursors, and their optical and electrical characterizations. We show the possibility to observe p-type conductivity in ZnSe due to a hole accumulation at the interface in the GaAs side. This is consistent with a simple model taking Into account the conduction and valence bands discontinuities at the ZnSe/GaAs interface.
INTRODUCTION Extensive studies have been performed on the epitaxial growth of ZnSe binary compound in view of its possible application for short wavelength optical devices. In recent years, the growth by both molecular beam epitaxy (MBE) and metalorganic vapor phase epitaxy (MOVPE) gave significant progress. It Is known that the wide band gap II-VI compounds have exhibited difficulties in achieving good bipolar conductivities. Generally, the selenides are found more easily n-type doped. It is the case of ZnSe in which the achievement of heavily n-type is now well established. An important subject of interest consists in the possibility to obtain high conductive p-type ZnSe, which is essential for the preparation of blue emitting electroluminescent diodes. In a recent paper [1] Neumark reviewed various reports in the past literature concerning the obtention of low resistivity p-type ZnSe (References are given in Neumark's paper). He noted that unfortunately the published works were not reproduced in other laboratories and/or some internal inconsistencies ( e.g. p-type behaviour via n-dopant, disagreement with semiconductor theory). His reevaluation of the past results concludes that the observed p-type in ZnSe materials were due to the role of large twinnings. This result assumes that the observed conductivity is really p-type. However the optical and electrical measurements were interpreted in terms of bulk material and neglected the important role payed by the ZnSe/GaAs interface of the heterostructure. Some informations on the band offset (2-51
Mat. Res. Soc. Symp. Proc. Vol. 198. Q1990 Materials Research Society
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indicate that the direct analysis of the experimental results (particulary Hall effect ) is not satisfactory and merits further investigations. This new look on the understanding of experimental results has been used principally in the case of n-ZnSe/n-GaAs heterostructure [6-8]. And yet some disagreements persist between the theorical predictions [2,51 and experimental results [6]. In this paper, we report the
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