InGaSb Defect Filter Layer to Improve Performance of GaSb Solar Cells Grown on GaAs Substrates
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https://doi.org/10.1007/s11664-020-08490-3 Ó 2020 The Minerals, Metals & Materials Society
InGaSb Defect Filter Layer to Improve Performance of GaSb Solar Cells Grown on GaAs Substrates A. MANSOORI,1,3 S.J. ADDAMANE,2 E.J. RENTERIA,1 D.M. SHIMA,1 and G. BALAKRISHNAN1 1.—Center for High Technology Materials, University of New Mexico, Albuquerque, NM, USA. 2.—Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, NM, USA. 3.—e-mail: [email protected]
The reduction of the threading dislocation density in metamorphic GaSb grown on GaAs substrates through the use of InGaSb defect filter layers has been investigated. More specifically, we study the effects of strain and thickness on the ability of a InGaSb defect filter layer to reduce threading dislocations in GaSb solar cells grown on GaAs substrates. The strain between the GaSb metamorphic layer on GaAs substrate (99.5% relaxed) and the InGaSb defect filter layer is varied by changing the indium composition in the InGaSb layer. It is demonstrated that an InGaSb defect filter layer with 0.6% strain is more effective for blocking threading dislocations compared with higher-strain layers, resulting in improved short-circuit current (Jsc) and open-circuit voltage (Voc) for the metamorphic GaSb solar cell. The optimization of the defect filter layer involves varying the thickness of the layer to achieve the lowest possible threading dislocation density. This also takes into account the critical thickness of the InGaSb layer on GaSb to avoid generation of threading dislocations from the InGaSb layer itself. It is shown that adding an In0.11Ga0.89Sb defect filter layer with thickness of 250 nm and 0.6% strain beneath a GaSb solar cell grown on a GaAs substrate improves Voc from 0.1 V to 0.16 V and Jsc from 19.7 mA/cm2 to 24.7 mA/cm2. Key words: Defect filter layer, interfacial misfit dislocation, GaSb solar cell, threading dislocation reduction
INTRODUCTION Group III–V compound semiconductor-based multijunction solar cells (MJSCs) have been shown to be the highest-efficiency photovoltaic devices for producing electrical energy from the sun.1,2 While single-junction solar cells have been restricted to efficiencies < 30%, MJSCs have been able to realize 39% without concentration and 46% under concentration.3,4 The reason for the increased performance of MJSCs over single-junction solar cells is the reduction of thermalization losses and the absorption of low-energy near-infrared photons.
(Received June 6, 2020; accepted September 15, 2020)
MJSCs are able to achieve this by monolithically stacking solar cells with different bandgaps from high to low, thus allowing for an optimal conversion of photons to electric power.5 However, MJSCs have some drawbacks, since the stacking of materials with different bandgaps requires the availability of lattice-matched alloys on commercially viable substrates. The most well-established sequence is the growth of lattice-matched alloys such as InGaP, AlGaAs, and GaAs on germanium substrates. However, the lac
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