133 ISSN 1063-7850, Technical Physics Letters, 2017, Vol. 43, No. 1, pp. 133–135. © Pleiades Publishing, Ltd., 2017. Original Russian Text © A. Yusupov, K. Adambaev, Z.Z. Turaev, S.R. Aliev, A. Kutlimratov, 2017, published in Pis’ma v Zhurnal Tekhnicheskoi Fiziki, 2017, Vol. 43, No. 2, pp. 98–103. Creation and Electrical Properties of p-Cu 2 ZnSnS 4 /n-Si Heterojunctions A. Yusupov a *, K. Adambaev a , Z. Z. Turaev b , S. R. Aliev c , and A. Kutlimratov d a Tashkent Automobile and Road Institute, Tashkent, 100060 Uzbekistan b Ulugbek National University of Uzbekistan, Tashkent, 100174 Uzbekistan c Andizhan State University, Andizhan, 710000 Uzbekistan d Physicotechnical Institute, Academy of Sciences of Uzbekistan, Tashkent, 100084 Uzbekistan *e-mail: ayus@mail.ru Received September 23, 2016 Abstract—Anisotype p-Cu 2 ZnSnS 4 /n-Si heterojunctions have been manufactured for the first type by sulfi- dation of base-metal layers predeposited onto polycrystalline silicon substrates. Current–voltage character- istics of the heterojunctions are analyzed, and the mechanisms of current transfer are discussed. It is estab- lished that forward-biased structures are characterized by both tunneling-recombination processes and space-charge limited mobility of carriers. In reversely biased heterojunctions, space-charge limited currents predominate. DOI: 10.1134/S1063785017010291 In recent years, increasing interest of researchers has been devoted to semiconductor heterojunctions, which possess some advantages in comparison to homojunc- tions. Heterojunctions are widely used in electronics and photovoltaics [1, 2]. Solar cells (SCs) based on het- erojunctions employ light-absorbing layers of semicon- ductors with high optical-absorption coefficients. Quaternary semiconductor compound Cu 2 ZnSnS 4 (CZTS) is a promising material for absorbing layers of SCs [3, 4]. CZTS is a direct-band semiconductor with a bandgap width of about 1.5 eV [1, 2], which pos- sesses a large absorption coefficient (~10 5 cm –1 ) [3, 4]. The component elements are widespread in nature, cheap, and nontoxic. In recent years, SCs with effi- ciencies from 5.4 to 12.6% have been created based on Cu 2 ZnSnS(Se) 4 compounds [5, 6]. Therefore, CZTS can be considered a promising candidate to replace indium–gallium compositions in thin-film SCs. CZTS-based SCs usually incorporate a CdS/Cu 2 ZnSnS 4 heterojunction as the barrier [5, 6]. However, taking into account modern ecological restrictions, it is necessary to exclude toxic cadmium from the SC composition. Therefore, the task appears of finding an alternative barrier junction for CZTS- based SCs. The present work is devoted to the creation and characterization of anisotype p-Cu 2 ZnSnS 4 /n-Si heterojunctions on polycrystalline silicon substrates. Thin CZTS layers on a polycrystalline Si substrate were formed in two stages. At the first stage, a base layer of components were formed on the substrate by vacuum deposition at a residual gas pressure of (3– 5) × 10 –5 Torr. At the second stage, the base layer was sulfided from an unlimited source in a closed volume. The CZTS layer was formed by thermal annealing of samples with base-metal layers at 400–620°C in ampoules for a period of time varying within 15– 90 min. Then, the temperature of annealed samples was reduced to 200°C at a rate of 10–15°C/min. Finally, the ampoules were extracted from the furnace and allowed to cool down to room temperature. The obtained films were characterized by measur- ing their electrical properties. All samples prepared without intentional doping exhibited hole (p-type) conductivity. This was probably related to the fact that CZTS-film formation is accompanied by the appear- ance of structural defects, such as vacancies of copper atoms (V Cu ) and copper atoms substituted for zinc in its nodes (Cu Zn ) [7]. The sheet resistance of CZTS films was within 30–55 Ω/sq. Stationary current–voltage (I–V) characteristics of obtained p-Cu 2 ZnSnS 4 /n-Si heterojunctions were measured at room temperature on samples with ohmic contacts formed by depositing indium–gallium eutec- tic alloy. Figure 1 shows the typical I(V) characteristic with forward and reverse branches plotted in various coordinates. As can be seen from Fig. 1a, the hetero- structure possesses clearly pronounced diode charac- teristics. The forward direction corresponds to positive polarity of the external bias voltage applied to the CZTS film, in agreement with the energy-band model of this heterojunction [8]. The rectification factors in