The Charge Carriers Transport Mechanism Through the Interface Layer of the p-GaSe(Cu)/n + GaAs Heterojunctions
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The Charge Carriers Transport Mechanism Through the Interface Layer of the pGaSe(Cu)/n+GaAs Heterojunctions Elmira I. Cuculescu1 and Mihail I. Caraman2 1 Physics, Moldova State University, 60 A. Mateevici str., Chisinau, MD 2009, Moldova 2 Engineering, University of Bacau, 157 Calea Marasesti, Bacau, 600115, Romania
ABSTRACT The photoelectrical properties of p-GaSe(Cu)/n-GaAs heterojunctions obtained by optically contacting the components and by thermal evaporation of GaSe, have been studied. The rectification factor for optically contacted heterojunctions is ∼2⋅102 at 5 V, and the current flow is determined by diffusion mechanism. The diffusion and recombination through the interface defects mechanisms determine de current flow for heterojunctions formed by GaSe evaporation. INTRODUCTION Gallium Selenide (GaSe) is often used as a passivation layer at the interface of GaAs [1] and Si [2] based heterojunctions due to relatively low density of the surface states. Relatively high conductive GaSe layers (σ≥10-3 Ω-1cm-1) are used as a base material for different optoelectronic devices, such as solar energy conversion elements, photodiodes, sensitive in a wide wavelength range [3]. In these structures optical contact to GaSe layers is used. GaSe layers, having thicknesses 6 V points at shunting sectors, being present due to GaSe macro defects presence. As one can see eU ⎛ ⎞ − 1⎟ equation, where I0 from figure 3 b, the I-U plot for U 10 V, dark as well for E=500 lx illumination differ from the exponential dependence and is determined by the redistribution of the voltage
drop on the contact barrier and series resistance determined by the GaSe layer and the defect nGaAs layers at the interface of the heterojunction. So, for high current densities, the I-U curve is determined by the series resistance. As stated above, the heterojunction have been obtained by depositing GaSe onto 710 K heated n-GaAs plates. As atomís emission in vacuum is present at high temperature and at the same time Se diffuse in GaAs layer. The replacement of the As atom with Se occur. As a result, a Ga2Se3 layer in formed at the interface[7]. As a result of annealing at 700÷710 K the thickness of Ga2Se3 increases. For Ga2Se3 layer formation, the As vacancies close to the contact surface is needed. The vacancies are formed as a result of thermal emission of the As atoms from the crystalís surface. At Ga2Se3 formation, along with three As atoms removal, one Ga binding atom diffuses to the surface through the stoichiometric vacancies of the as-formed layer. In Ga2Se3 one third part of the Se sublattice are vacancies [13], so this diffusion mechanism is possible, considering similarity of the covalent radii of Se and As ñ 1.16 ≈ and 1.20 ≈ respectively [14]. The excess of Ga atoms at the upper surface of the structure leads, probably, to the formation of Ga2Se phase as well. So, the presence of the structural defects in the interface layer determines the relative high value of the diodic factor n≈1.7 determined from I-U plots. Additional info
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