photovoltage trancients of Si-DOPED InAs/GaAs SOLAR CELLS with AlAs CAP LAYERS

O.O. Kozak1, S.V. Kondratenko1, Yu.I. Mazur2, Yu. Maidaniuk2, P. Lam3, M. Tang3, J. Wu3, H. Liu3 and G.J. Salamo2

1 Department of Physics, Taras Shevchenko National University of Kyiv, 64 Volodymyrska St., 01601, Kyiv, Ukraine,  e-mail: kozakaleksei@univ.kiev.ua
2Institute for Nanoscience and Engineering, University of Arkansas,
Fayetteville, Arkansas 72701, United States of America
3Department of Electronic and Electrical Engineering, University College London,
Torrington Place, London WC1E 7JE, United Kingdom

The concept of intermediate band solar cells has been developed as a method of enhancing the photoelectric conversion efficiency [1]. Incorporation of quantum dots (QDs) into the space-charge layer of pin diodes is promising for expansion of the spectral response to the IR range and increase of the short-circuit current without loss in the open-circuit voltage [2].
In this work, we have studied the effect of AlAs/InAs QDs in the space-charge region of GaAs p-i-n diodes on recombination and photogeneration processes using photovoltage transient techniques. Figure 1 shows structure of the Si-doped InAs/GaAs p-i-n diodes with AlAs/InAs QDs (a) and photovoltage transients of the samples with different concentration of Si impurities measured at 300 K (b). 
(a)	                                                       (b)
      
Figure. 1. (a) Structure of the Si-doped InAs/GaAs p-i-n diodes with AlAs/InAs QDs. (b) Room temperature photovoltage transients of the samples with different concentration of Si impurities.

We have found that together with the enhanced photoresponse in the IR range, applying Si dopants to AlAs/InAs QDs significantly decreases the recombination losses via QDs, thereby, prolongs the photovoltage decay. As shown on inset to Fig.1b, time constant derived from PV decay curves increased nonmonotonically with increasing Si concentration in QD. The observed changes in PV decay times caused by appearance of the local electric fields in and around QDs.

[1] A. Luque, A. Marti, Phys. Rev. Lett. 78, 5014–5017 (1997).
[2] S. Kondratenko et all, J. Phys. D: Appl. Phys. 50, 165101 (2017).