Single microcrystals of Cu2GeS3 (CGS) were grown in molten LiI salt. According to x-ray diffraction measurements, all of the samples were made up entirely of CGS crystals. Raman spectra and photoluminescence (PL) at room temperature revealed two different types of crystals. Type A crystals displayed an asymmetric PL band at about 1.57 eV, while type B crystals displayed extra bands at 1.673, 1.587, and 1.474 eV. Raman spectra of both types were also different. The existence of two band-to-band recombinations, connected to split valence bands V1 and V2, is one explanation for the shape of the type B PL spectrum. It was discovered that the spin–orbit splitting energy was 0.11 eV. PL bands at 1.474 and 1.587 eV were related to acceptor levels coupled with V1 and V2 valence bands, respectively. For the V2 valence band, the depth of the resonant acceptor state was 0.09 eV. The acceptor level linked to the V1 valence band was also found to have the same value. To measure external quantum efficiency (EQE) spectra, monograin solar cells made from our microcrystals were used. The derivative of the EQE spectrum results in two distinct peaks, split by 0.11 eV. The inflection point minima are at 1.62 and 1.73 eV. We propose a model for various energy levels based on these findings.

中文翻译：

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Cu2GeS3 微晶中价带分裂和谐振受体态的光学研究


Cu2GeS3 （CGS） 的单微晶在熔融的 LiI 盐中生长。根据 X 射线衍射测量，所有样品都完全由 CGS 晶体组成。室温下的拉曼光谱和光致发光 （PL） 揭示了两种不同类型的晶体。A 型晶体在大约 1.57 eV 处显示出不对称的 PL 带，而 B 型晶体在 1.673、1.587 和 1.474 eV 处显示出额外的条带。两种类型的拉曼光谱也不同。存在两个带间复合，连接到分裂价带 V1 和 V2，这是对 B 型 PL 光谱形状的一种解释。发现自旋-轨道分裂能量为 0.11 eV。1.474 和 1.587 eV 的 PL 带分别与受体水平以及 V1 和 V2 价带相关。对于 V2 价带，谐振受体态的深度为 0.09 eV。与 V1 价带相连的受体水平也被发现具有相同的值。为了测量外部量子效率 （EQE） 光谱，使用了由我们的微晶制成的单晶太阳能电池。EQE 光谱的导数产生两个不同的峰值，被 0.11 eV 分割。拐点最小值分别为 1.62 和 1.73 eV。基于这些发现，我们提出了一个适用于各种能级的模型。