针对低激发功率密度光致发光(photoluminescence, PL)谱信噪比(signal-to-noise ratio, SNR)对GaAs1-xBix 带尾能级探究的限制问题, 基于傅里叶变换红外PL光谱实验系统对两个GaAs1-xBix 外延膜开展变激发光斑尺寸PL光谱测试分析.结果表明, 激发功率恒定时光斑直径增大导致PL峰位红移和线宽先降低后增大.这一现象是由于等效激发功率密度的降低而导致的.在保持激发功率密度为5.1 W/mm2时, 光斑增大不影响光谱线型但显著提升SNR.由此, 低激发功率密度PL光谱的弱信号探测能力得以提高, 有助光谱定量拟合分析.本工作表明, 适当增大激发光斑尺寸有助于低激发功率密度PL光谱的SNR和弱信号分辨能力的提升.

Low excitation-power density photoluminescence (PL) spectra suffered from poor spectral signal-to-noise ratio (SNR)and hence restricted the study of the band-tail states in GaAs1-xBix. We conduct laser spot-size-dependent PL measurements on two GaAs1-xBix epitaxial films by Fourier transform infrared spectrometer-based PL system with enhanced sensitivity. It is observed that (i) with constant excitation power, increase of laser-spot diameter leads to a redshift of the PL-peak position and a linewidth evolution of first decreasing and then increasing, which is attributed to the decrease of the equivalent excitation power density, and (ii) with a constant excitation power density of 5.1 W/mm2, the PL lineshape is unchanged while the SNR is significantly improved as the laser spot diameter rises. As a result, the weak transition features are well resolved in the PL spectra taken at low excitation power density, and can be safely treated by spectral fitting analysis. The result indicates that adequate increase of excitation spot-size contributes to the improvement of the SNR and sensitivity as well for PL measurement at low excitation-power density.