Electrical Properties of Heavily Be-doped GaAs grown by Molecular Beam Epitaxy
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ELECTRICAL PROPERTIES OF HEAVILY Be-DOPED GaAs GROWN BY MOLECULAR BEAM EPITAXY H. SHIBATA-, Y. MAKITA-, A. YAMADA-, N. OHNISHI--, M. MORI*, Y. NAKAYAMA*, A. C. BEYE*, K. M. MAYER-, T. TAKAHASHI*, Y. SUGIYAMA-, M.TACANO2 , K. ISHITUKA*2 * and T. MATSUMORI**`2 * Electrotechnical Laboratory, 1-1-4 Umezono, Tsukuba-shi, 305 Japan. ** Informex Incorporated Limited, 3-15-10 Hiyoshi, Kohoku-ku,
Yokohama-shi,
225 Japan.
*** Nippon Institute of Technology,
4-1 Gakuendai, Miyashiro-machi, Saitama-ken, 345 Japan. **** Tokai University, 1117 Kitakaname, Hiratsuka-shi, 259-12 Japan. ABSTRACT Electrical properties of heavily Be-doped GaAs grown by molecular beam epitaxy were investigated systematically in a wide range of Be-concentration from lX 1014 up to 2X 1020 cm- 3 by using yan der Pauw technique. Probable carrier scattering mechanisms observed in this work are discussed by taking into account the radiative mechanisms of several new photoluminescence emissions previously observed in the band-edge-emission region of the samples. All samples were checked their electrical properties first at roomtemperature. Five selected samples out of them were measured from 10* K up Samples having the carrier concentration from 1014 to to room-temperature. 1018 cm- 3 presented typical semiconductor-like conduction with finite carrier excitation energy. For samples having carrier concentration 7X 1016 cm -3, the conduction mechanism at high temperature region above 30* K was dominated by holes thermally excited into valence band. At low temperature region below 300 K , it was dominated by holes hopping from neutral to ionized acceptors with the assistance of phonons. Hole mobilities of samples having the carrier concentration from 1017 to 1018 cm- 3 showed an anomalous behavior in the low temperature region, which suggests the presence of a new type of carrier scattering mechanism. A radiative center denoted by [g-gj observed ii this concentration region will be a candidate scattering center to explain these electrical behaviors. Samples having the carrier concentra3 tion larger than 1019 cm- demonstrated typically metallic electric conduction not owing to thermally excited carriers, which means that an impurity band is formed but merged with valence band. The density of state of this combined valence band mixed with impurity band can be supposed to reflect carrier concentration dependence of the PL emission bands observed in this region, i.e. [g-gla , [g-gL] and [g-g]y INTRODUCTION Systematic study on both optical and electrical properties of impurity doped GaAs for a wide range of impurity concentration is necessary for the fabrication of opto-electronic devices. Photoluminescence (PL) is one of the most important optical properties of semiconductors, but intrinsic PL features of p-type GaAs have not yet been revealed sufficiently compared with those of n-type GaAs, particularly in the heavily-doped regime Il1. In the near-band-edge emission region, a blue shift of the main broad PL emission with increasing donor concentration ([Dl) ha
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