The optical absorption coefficient is one of the fundamental properties of semiconductors and is critical to the development of optical devices. Herein, a revival of the constant photocurrent method is presented to measure sub‐bandgap absorption in wide bandgap semiconductor films. The method involves maintaining a constant photocurrent by continually adjusting the impinging photon flux across the energy spectrum. Under such conditions, the reciprocal of the photon flux for uniformly absorbed light is proportional to the absorption coefficient. This method is applied to α‐Ga2O3 and reveals that it can access the absorption coefficient from 1 × 105 cm−1 at the band edge (5.3 eV) to 0.8 cm−1 close to mid‐bandgap (2.7 eV). Changes in the steepness of the absorption curve in the sub‐bandgap region are in excellent agreement with defect states of α‐Ga2O3 reported by deep level transient spectroscopy, indicating that the technique shows promise as a probe of energetically distributed defect states in thin film wide bandgap semiconductors.

中文翻译：

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恒定光电流法探测宽带隙半导体薄膜中的亚带隙吸收：以 α-Ga2O3 为例

光吸收系数是半导体的基本特性之一，对于光学器件的开发至关重要。在此，提出了恒定光电流方法的复兴来测量宽带隙半导体薄膜中的子带隙吸收。该方法包括通过不断调整整个能谱的撞击光子通量来维持恒定的光电流。在这种条件下，均匀吸收光的光子通量的倒数与吸收系数成正比。该方法适用于α-Ga2氧3并表明它可以从 1 × 10 获得吸收系数5厘米−1在能带边缘 (5.3 eV) 至 0.8 cm−1接近中带隙（2.7 eV）。亚带隙区域吸收曲线陡度的变化与 α-Ga 的缺陷态非常一致2氧3深能级瞬态光谱报道表明，该技术有望作为薄膜宽带隙半导体中能量分布缺陷态的探针。