Nitrogen Concentration Dependence of Two‐Step Photocurrent Generation by Below‐Gap Excitation in GaPN Alloys

Two‐step photocurrent generation and its dependence on nitrogen concentration in GaPN alloys using two‐wavelength excited photocurrent (TWEPC) measurements are investigated. External quantum efficiency (EQE) measurements show an increase in the two‐step absorption of below‐gap excitation light through tail states at longer wavelengths and that the quasi‐direct gap redshifts as the nitrogen concentration increases. The improvement in the EQE at longer wavelengths is explained by the increased density of the tail states in GaPN with higher nitrogen concentrations. In contrast, the EQE decreases at shorter wavelengths with increasing nitrogen content. TWEPC results show that differential photocurrent density , which shows the synergy effect of multiple‐wavelength light, reduces with the addition of nitrogen. It is found from rate–equation analysis that the decrease in the EQE at shorter wavelengths and in is mainly due to the increased nonradiative recombination in GaPN with higher nitrogen concentration. The use of lattice‐matched alloys and a p‐type GaP capping layer as well as the optimization of the growth conditions can improve the EQE at shorter wavelengths and .