Spectral Change of E- Band Emission in a GaAs:N delta-Doped Superlattice Due to Below-Gap Excitation and Its Discrimination from Thermal Activation

摘要

In this study, we examined the E- band luminescence of a GaAs:N delta-doped superlattice (SL) grown by metal organic vapor phase epitaxy with 0.15% nitrogen (N) using two-wavelength excited photoluminescence. It was observed that the photoluminescence (PL) intensity of the low-energy peak (P-2) at 1.38 eV of the E- band was quenched larger compared to the high-energy peak (P-1) at 1.41 eV. This was due to the superposition of below-gap excitation (BGE) light of energy 0.95 eV over the above-gap excitation light of energy 1.45 eV on the SL structure at a fixed temperature of 12 K. On the other hand, at higher temperatures, the PL intensity of the high-energy peak P-1 was quenched higher compared to the low-energy peak P-2 without any addition of the BGE light. We interpreted the experimental results by considering the carrier recombination (CR) model and concluded that the observed PL spectral and intensity change of the E- band emission due to BGE does not result from the thermal activation, but from the optical excitation among the E- band, conduction band, and CR levels in GaAs:N delta-doped structure. We concluded that to achieve high-efficiency intermediate band-type solar cells, it is essential to understand the CR mechanism through CR levels by determining their origin and eliminating them from the material.