Archives of Electrical Engineering (Dec 2019)
Application of poly-energy implantation with H+ ions for additional energy levels formation in GaAs dedicated to photovoltaic cells
Abstract
The aim of this article is to present the results of research aimed at confirmation whether it is possible to form an intermediate band in GaAs implantation with H+ ions. The obtained results were discussed with particular emphasis on possible applications in the photovoltaic industry. As it is commonly known, the idea of intermediate band solar cells reveals considerable potential as the most fundamental principle of the next generation of semiconductors solar cells. In progress of the research, a series of GaAs samples were subjected to poly-energy implantation of H+ ions, followed by high-temperature annealing. Tests were conducted using thermal admittance spectroscopy, under conditions of variable ambient temperature, measuring signal frequency in order to localize deep energy levels, introduced by ion implantation. Activation energy ΔE was determined for additional energy levels resulting from the implantation of H+ ions. The method of determining the activation energy value is shown in Fig. 2 and the values read from it are σ0 = 10−9 (Ω·cm)−1 for 1000/T0 = 3.75 K−1 and σ1 = 1.34 × 10−4 (Ω·cm)−1 for 1000/T1 = 2.0 K−1. As a result, we obtain ΔE ≈ 0:58 eV. It was possible to identify a single deep level in the sample of GaAs implanted with H+ ions. Subsequently, its location in the band gap was determined by estimating the value of ΔE. However, in order to confirm whether the intermediate band was actually formed, it is necessary to perform further analyses. In particular, it is necessary to implement a new analytical model, which takes into consideration the phenomena associated with the thermally activated mechanisms of carrier transport as it was described in [13]. Moreover, the influence of certain parameters of ion implantation, post-implantation treatment and testing conditions should also be considered.
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