Dark Current Analysis of InAs/GaSb Type II Superlattice Infrared Detectors

The infrared imaging performance of type-II superlattice (T2SL) has been widely used in civil and aerospace fields. Due to the special band structure and material properties, the T2SL has the advantages of the adjustable bandgap, a wide range of spectral response (2– $30~\mu \text{m}$ ), effectively inhibiting Auger recombination, low cost, and good uniformity in large areas. InAs/GaSb T2SL is considered to be a promising material to advance the performance of photoelectric devices, especially in the long-wave range. With the development of science and technology and the continuous efforts of scientists, the T2SL has made great progress in material growth, device design, and process research. However, there is still a gap to the theoretically values. This article discusses the reasons for the performance degradation of T2SL devices, especially the surface and bulk dark current factors, and introduces various methods to reduce dark current and advantages and disadvantages of these methods.

I. Introduction

In 1970, Esaki and Tsu [1] first proposed the concept of the antimonide-based superlattice. Subsequently, researchers studied superlattice in-depth. In 1987, Smith and Mailhiot [2] proposed the application of InAs/GaSb type-II superlattice (T2SL) to infrared detectors. Since then, T2SL has become a research hot spot in the field of infrared detectors. At present, infrared detection technology has entered the third-generation development stage. The mainstream infrared detectors include mercury cadmium telluride (MCT), quantum well-infrared photodetectors (QWIP), and T2SL infrared detectors [3]. Among them, the widely studied infrared detector material is MCT, which has successfully developed a variety of response bands and excellent performance of the unit and array devices [4]. The dark current of the MCT infrared detector is relatively small, and the quantum efficiency (QE) is high. However, MCT has some disadvantages in the material itself. For example, the covalent bond between Hg and Te is weak, so the material has poor stability and radiation resistance, especially in long-wave applications with more such kinds of covalent bonds. The components are prone to segregation during the growth process, which makes the uniformity of material worse and makes it difficult to realize the application of a large array [5]. The QWIP is achieved through intersubband transitions of electrons and holes confined in the quantum well. When infrared light irradiates the quantum well, electrons absorb the infrared energy and transition from the ground state to the excited state, realizing photoelectric conversion. The bandgap of quantum well semiconductor materials can be tuned by varying the thickness and composition of the materials. Due to the requirement of incident direction of infrared radiation on quantum well materials, the QE of quantum well materials is one of its major disadvantages. However, this issue can be improved later by forming polarized light with gratings, but it will increase the processing difficulty of device fabrication. T2SL has the advantages of adjustable energy band [6], [7], [8], [9], wide spectral response range (2–) [10], [11], [12], [13], physical separation of electrons and holes in space [2], large effective mass of electrons, and good material uniformity [14]. It meets the requirements of the third-generation detector for high performance, large array [15], [16], multicolor detection [17], [18], [19], and low cost. It may be the preferred material of the new generation of infrared detectors, attracting more and more attention [20].