Abstract
This work reports fabrication details of heterojunction diodes and solar cells obtained by sputter deposition of amorphous GaAs on p-doped single crystalline Si. The effects of two additional process steps were investigated: A hydrofluoric acid (HF) etching treatment of the Si substrate prior to the GaAs sputter deposition and a subsequent annealing treatment of the complete layered system. A transmission electron microscopy (TEM) exploration of the interface reveals the formation of a few nanometer thick SiO2 interface layer and some crystallinity degree of the GaAs layer close to the interface. It was shown that an additional HF etching treatment of the Si substrate improves the short circuit current and degrades the open circuit voltage of the solar cells. Furthermore, an additional thermal annealing step was performed on some selected samples before and after the deposition of an indium tin oxide (ITO) film on top of the a-GaAs layer. It was found that the occurrence of surface related defects is reduced in case of a heat treatment performed after the deposition of the ITO layer, which also results in a reduction of the dark saturation current density and resistive losses.
Highlights
GaAs/Si heterojunctions could allow cost reduction and integration of fast electronic and optical devices on Si in different fields of electronics and have been of interest to the materials science community since the 1980s
In this work we describe fabrication details of diodes and solar cells prepared by sputter deposition of n-type GaAs on p-type single crystalline Si (c-Si) wafers focusing our research on two varying process steps: An hydrofluoric acid (HF)
Further J-V curves of a-GaAs/c-Si heterojunction were measured at different temperatures ranging from 286.8 K to 448 K using an HP4124B DC source/monitor system
Summary
GaAs/Si heterojunctions could allow cost reduction and integration of fast electronic and optical devices on Si in different fields of electronics and have been of interest to the materials science community since the 1980s. Graded SiGe layers, prepared by chemical vapor deposition (CVD), molecular beam epitaxy (MBE) or low-energy plasma enhanced CVD (PECVD), were used as buffers between Si and GaAs in order to reduce the lattice mismatch [9,10,11,12,13]. Schottky barrier solar cells and diodes as well as GaAs/Si heterojunctions fabricated by magnetron sputter deposition techniques were reported in the past [20,21]. Magnetron sputtering allows the deposition of thin GaAs films with good quality at low temperatures [22], which makes this technique interesting for large scale solar cell fabrication. We are dealing with GaAs/Si based solar cells analyzing their photoelectrical behavior with respect to different preparation recipes (photo current behavior)
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