Abstract
Point defects in high-purity GaN layers grown by hydride vapor phase epitaxy are studied by steady-state and time-resolved photoluminescence (PL). The electron-capture coefficients for defects responsible for the dominant defect-related PL bands in this material are found. The capture coefficients for all the defects, except for the green luminescence (GL1) band, are independent of temperature. The electron-capture coefficient for the GL1 band significantly changes with temperature because the GL1 band is caused by an internal transition in the related defect, involving an excited state acting as a giant trap for electrons. By using the determined electron-capture coefficients, the concentration of free electrons can be found at different temperatures by a contactless method. A new classification system is suggested for defect-related PL bands in undoped GaN.
Highlights
We have demonstrated that time-resolved PL can be a powerful tool to determine the concentration of free electrons and the concentration of point defects in semiconductors[14]
The coefficient CnA is determined for the ultraviolet luminescence (UVL), blue luminescence (BL1), green luminescence (GL1), yellow luminescence (YL1), and red luminescence (RL1) bands
We have established that the electron-capture coefficients for the UVL and BL1 bands in nondegenerate and degenerate GaN are independent of temperature from 40 to 100 K and from 40 to 180 K
Summary
We have demonstrated that time-resolved PL can be a powerful tool to determine the concentration of free electrons and the concentration of point defects in semiconductors[14]. In order to find the concentration of free electrons from time-resolved PL measurements, the electron-capture coefficients (CnA) for the defect-related PL bands must first be found. We add the number 1 to the commonly used abbreviations to identify a defect-related band with specific properties, because more than one defect can cause red, yellow, green, and blue bands in undoped GaN. The calculated concentrations of free electrons at selected temperatures in several samples are compared with values obtained from temperature-dependent Hall-effect measurements. The knowledge of these capture coefficients allows us to find the concentration of free electrons in GaN; in particular, in regions not accessible by other techniques, such as the region close to the GaN/sapphire interface
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