Specific features of photoconductivity spectra of the CdTe/CdHgTe epitaxial graded-gap heterostructures
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CONDUCTOR STRUCTURES, INTERFACES, AND SURFACES
Specific Features of Photoconductivity Spectra of the CdTe/CdHgTe Epitaxial Graded-Gap Heterostructures A. I. Vlasenko and Z. K. Vlasenko^ Lashkarev Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Kiev, 03028 Ukraine ^e-mail: [email protected] Submitted March 17, 2005; accepted for publication April 20, 2005
Abstract—Based on studies the structural and photoelectric properties of CdTe/CdHgTe graded-gap heterostructures, it is found that the metallurgical interface between the materials, which is located in the structure bulk, is enriched with structural defects. An increased recombination rate is characteristic of this interface. This circumstance is the cause of the loss of photosensitivity in the mid-IR range of the broadband photoconductivity spectra of these heterostructures. For the epitaxial layers thinner than 10–20 µm, the effect of the metallurgical interface can manifest itself in the reduction or complete loss of photosensitivity. PACS numbers: 73.50.Pz, 73.50.Gr, 73.61.Ga DOI: 10.1134/S1063782606010088
1. INTRODUCTION For remote monitoring of processes and objects using the reflectance and emittance of the material, it is reasonable to use the broadband or multiband photodetectors. This circumstance is associated with the fact that the reflective properties of the objects are studied in the visible and near-infrared (near-IR) spectral regions, while the emissive properties are studied in the midand far-IR spectral regions [1, 2]. Conventionally, this issue is solved by design of “sandwiches” made from the layers or wafers of semiconductors with various band gaps Eg. These systems have a series of obvious disadvantages, particularly, high optical loss due to reflection and scattering at the boundaries, substantial stresses, accelerated degradation, etc. The structures with a steep composition gradient, which provide photosensitivity in a broad spectral range, are to a large extent devoid of these disadvantages [3]. Specifically, for the spectral region 0.8–15 µm, these are the CdTe/CdHgTe-based epitaxial graded-gap heterostructures. However, their use gives rise to the problem of the effect of the geometric interface between the starting materials, the so-called metallurgical interface, on the photoelectric characteristics of these heterostructures. For example, it was shown that this interface is saturated with structural defects of various physicochemical nature, which can lead to a substantial loss of photosensitivity of the devices or to the distortion of their spectral characteristics [4, 5]. It is possible that it is precisely the effect of the metallurgical interface that causes poor electrical and photoelectric parameters of these structures compared with
the bulk material, which was repeatedly mentioned in previous publications (see, for example, [6]). This study is devoted to the role of the metallurgical interface in the formation of spectral characteristics of photoconductivity of the CdTe/CdHgTe epitaxial graded-ga
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