Dilute nitrides heterostructures grown by liquid phase epitaxy for solar cells applications

In this paper, we present a study on liquid phase epitaxy (LPE) grown dilute nitride GaAsSbN layers and p-i-n heterostructures for use in multijunction solar cells. The composition of the layers and chemical bonding of Sb and N in the compounds were determined by energy- dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). The electrical properties of the grown samples were characterized by Hall effect measurements. Nominally undoped layers are n-type with Hall carrier concentration of 5 × 10¹⁶cm^-3. Mg was successfully used as acceptor dopant for obtaining closely compensated layers with electron concentration of 10¹⁵ cm^-3 as well as p-type layers with high free hole concentrations in the range (5-7) × 10¹⁸cm^-3. Temperature-dependent photoluminescence spectra at low and high excitation were measured to evaluate the optical quality and identify localized states in the grown layers. Non-contact surface photovoltage method provided information about the absorption characteristics of the GaAsSbN layers. A series of GaAs/GaAsSbN/GaAs heterostructures based on closely compensated i-GaAsSbN have been also grown by LPE. The red limit of the structures determined from surface photovoltage measurements was extended down to 1.2 eV. Single junction p-i-n solar cells with area 0.16 cm² were performed based on the grown structures. A power conversion efficiency of 4.1 % was measured for the fabricated cells under AM1.5 air global conditions.