Narrow bandgap (< 0.5 eV) colloidal semiconductor nanocrystals (e.g. mercury chalcogenides) provide practical platform for next generation short wave infrared, mid wave infrared and long wave infrared optoelectronic devices. Until now, most of the efforts in the field of infrared active nanocrystals have been taken on synthesizing nanocrystals, determining quantum states and building different geometry for optoelectronic devices. However, studies on interface trap states in the devices made from these narrow band gap nanocrystals are mostly unexplored. Herein, we investigate the defects or traps in these nanocrystals - embedded devices, which will be critical for improving their optoelectronic performance. In this article, we fabricate HgTe nanocrystals/TiO2 based photovoltaic devices and used capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) to investigate and obtain quantitative information on deep level trap states. Interestingly, frequency dependent C-V measurements show two peaks in the capacitance at lower frequency (< 40 kHz), which is attributed to the presence of trap states. However, at high frequency the presence of a weak hump-like structure almost at the center of above two peaks validate the role of interface traps. DLTS studies show that traps at the interface of HgTe nanocrystals/TiO2 acts as recombination centers having activation energies of 0.27, 0.4 and 0.45 eV with corresponding trap densities of 1.4×10^10, 1.9×10^11 and 1.5×10^11 〖cm〗^(-3) and estimated capture cross-sections of 6.3×10^(-14), 7.5×10^(-17) and 3.7×10^(-14) 〖cm〗^2, respectively. In this work, DLTS has revealed the existence of interface trap states and the frequency dependent capacitance measurements corroborate the effect of charge storage on the heterostructures built from these nanocrystals that helps in the development of futuristic devices.

中文翻译：

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基于HgTe纳米晶/TiO2异质结的短波红外光伏器件缺陷研究

窄带隙（< 0.5 eV）胶体半导体纳米晶体（例如汞硫族化物）为下一代短波红外、中波红外和长波红外光电器件提供了实用的平台。到目前为止，红外活性纳米晶体领域的大部分工作都集中在纳米晶体的合成、量子态的确定和光电器件的不同几何结构的构建上。然而，对由这些窄带隙纳米晶体制成的器件中界面陷阱态的研究大多未被探索。在这里，我们研究了这些纳米晶体中的缺陷或陷阱 - 嵌入式设备，这对于提高其光电性能至关重要。在本文中，我们制造了基于 HgTe 纳米晶体/TiO2 的光伏器件，并使用电容-电压 (CV) 和深能级瞬态光谱 (DLTS) 来研究和获得有关深能级陷阱态的定量信息。有趣的是，频率相关的 CV 测量显示较低频率 (< 40 kHz) 下的电容有两个峰值，这归因于陷阱态的存在。然而，在高频下，几乎在上述两个峰中心的弱驼峰状结构的存在验证了界面陷阱的作用。DLTS 研究表明，HgTe 纳米晶/TiO2 界面处的陷阱作为复合中心，其活化能分别为 0.27、0.4 和 0.45 eV，相应的陷阱密度分别为 1.4×10^10、1.9×10^11 和 1.5×10^11 〖 cm]^(-3) 和估计的捕获截面为 6.3×10^(-14)、7.5×10^(-17) 和 3。分别为 7×10^(-14) 〖cm〗^2。在这项工作中，DLTS 揭示了界面陷阱态的存在，并且频率相关的电容测量证实了电荷存储对由这些纳米晶体构建的异质结构的影响，这有助于开发未来设备。