Potential of using the Cd 0.8 Hg 0.2 Te alloy in solar cells
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ICS OF SEMICONDUCTOR DEVICES
Potential of Using the Cd0.8Hg0.2Te Alloy in Solar Cells L. A. Kosyachenko^, V. V. Kulchinsky, S. Yu. Paranchych, and V. M. Sklyarchuk Chernovtsy National University, Chernovtsy, 58012 Ukraine ^e-mail: [email protected] Submitted March 30, 2006; accepted for publication April 19, 2006
Abstract—Surface-barrier diodes based on the CdxHg1 – xTe alloy (x ≈ 0.8) sensitive in the wavelength range 0.3–1.1 µm, which were obtained by etching (bombardment) of the surface of the p-type crystal with argon ions, are studied. Using the measured spectral absorption and reflection curves, as well as the parameters of the diode structure, which were found from electrical characteristics, the spectra of photoelectric quantum efficiency of diodes are calculated. The results of the calculation of photoelectric parameters of the Gd0.8Hg0.2Te-based diodes are given in comparison with the CdTe-based and Si-based solar cells. For the AM1.5 solar irradiation conditions, the open-circuit voltage and short-circuit current, as well as values of limiting efficiency, are determined. PACS numbers: 73.30.+y, 78.66.Hf, 84.60.Jt DOI: 10.1134/S1063782607010186
conductor over the entire range x = 0–1, and thin-film solar cells based on the wide-gap CdxHg1 – xTe alloy (0.87 < x < 1) can be fabricated by the simple and inexpensive electrochemical deposition method [4, 5]. In this paper, we report the results of studying the photovoltaic surface-barrier diode structures based on the CdxHg1 – xTe alloy (x = 0.8) with the band gap close to Eg = 1.1 eV, i.e., corresponding to the lower boundary of the above-mentioned range 1.1–1.5 eV. The band-to-band transitions in such a semiconductor encompass a larger part of the solar-radiation spectrum than CdTe; therefore, in what follows, we compare the absorptivity of these semiconductors. Since the energy 1.1 eV coincides with the Si band gap, it is also of interest to compare the absorptivity of the Cd0.8Hg0.2Te alloy and Si. The presented results of studies allow us to determine the most important characteristics of the solar cell, which are, in particular, the width of the space charge region (DCR) of the diode, and the carrier lifetime. The results of calculation of the charge-collection efficiency and the efficiency factor of the Cd0.8Hg0.2Te-based diode structures are also presented.
1. INTRODUCTION The CdxHg1 – xTe semiconductor alloy (x = 0.2–0.3) is the most important material of infrared photoelectronics operating in the spectral regions 3–5 µm and, especially, 8–14 µm, which correspond to atmospheric “transparency windows.” Since the binary compounds HgTe and CdTe form a continuous series of solid solutions at each component ratio, the CdxHg1 – xTe alloy with an increased CdTe content can be used in the short-wavelength region up to the wavelength λ = 0.83 µm, which corresponds to the CdTe band gap (Eg = 1.46 eV at T = 300 K). From the practical viewpoint, the CdxHg1 – xTe alloys with x = 0.7 and x = 0.6 are attractive. The use of these alloys allows one to obtain the
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