Photovoltaic Effect in the Anisotype GaSe-InSe Heterojunctions Under Pressure
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Photovoltaic Effect in the Anisotype GaSe-InSe Heterojunctions Under Pressure S.I. Drapak, M.O. Vorobets and Z.D. Kovalyuk I.M. Frantsevich Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, Chernivtsi Department, 5 Iryna Vilde Str., 58001, Chernivtsi, Ukraine. ABSTRACT The influence of mechanical pressure along the direction across the interface of n-InSe-pGaSe heterojunctions on saturation photo-e.m.f. and short-circuit current is investigated. It is shown that at the InSe/GaSe optical contacts subjected to a pressure P = 35-40 kPa an increase of the open-circuit voltage nearly twice and short-circuit current more than by a factor of five in comparison to the initial samples takes place. It makes possible to predict a possibility of considerable increasing photoconversion efficiency of such structures.
INTRODUCTION Photodiodes based on anisotype n-InSe-р-GaSe heterojunctions prepared by the method of direct optical contact [1] are analogues to Si-based structures operating at high radiation conditions [2]. The photoconversion efficiency of such heterojunctions (HJ) is between 0.3 and 3.2 % depending on electrical parameters of the contacting materials and construction peculiarities of the structures [3]. According to [4], InSe/GaSe heterocontact is a semiconductorinsulator-semiconductor structure, where, on contrary to a generally accepted opinion that cleaved surfaces of layered semiconductors are inert to sorption of foreign atoms from the atmosphere [5], the interfacial layer of oxygen acts as dielectric. It is in a non-equilibrium state with long-term relaxation. As it is shown in [4], during long-term keeping for 10 to 14 years due to diffusive spreading oxygen the contact of InSe and GaSe semiconductor plates becomes closer and its area is only of about 10 % of the total area of the HJ. If to estimate the efficiency of such the structures taking into account the real area (in a close contact), its value for the HJ based on gallium and indium selenides with optimum parameters increases from 3.2 to 11-12 %. In the case when the existence of the close InSe/GaSe contact is a result of the “removal” of “air interlayer” or “filming” adsorbed atoms aggregates affected by the weight of the contacting semiconductors it is desirable to investigate the effect of pressure on photoconversion parameters of InSe/GaSe optical contact. Here we present the results of the preliminary investigations on influence of uniaxial pressing an InSe/GaSe optical contact on saturation photo-e.m.f. (opencircuit voltage) Voc and short-circuit current Isc.
EXPERIMENTAL DETAILS AND DISCUSSION Unfortunately, at the moment of the investigations there were no crystals of indium and gallium selenides appropriates for preparation of heterocontacts with the maximum efficiency (pGaSe = 5⋅1016 cm-3, nInSe =5⋅1015 cm-3, series resistance of the structure Rs 55-60 kPa is, probably, caused by the lattice mismatch of the contacting semiconductors (∼8 %) that begins to have an effect at decreasing the dielectr
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