(NH[sub 4])[sub 2]S[sub x]-Treated AlGaN MIS Photodetectors with LPD SiO[sub 2] Layer

Abstract

͑NH 4 ͒ 2 S x treatment was employed to enhance the efficiency of AlGaN metal-insulator-semiconductor ͑MIS͒ photodetectors ͑PDs͒ with a liquid phase deposited ͑LPD͒ SiO 2 layer. With ͑NH 4 ͒ 2 S x treatment, one can reduce the reverse leakage current of the PD by 2 orders of magnitude and enhance the effective Schottky barrier height from 0.77 to 0.86 eV. Also, the ͑NH 4 ͒ 2 S x treatment can also significantly reduce the interface state density, D it , at the AlGaN/LPD oxide interface. Photo-to-dark current ratio observed from the PDs with ͑NH 4 ͒ 2 S x treatment was also significantly larger.GaN-based semiconductor materials have been successfully used in high power, high frequency electronic devices and UV photodetectors ͑PDs͒ due to their excellent properties such as a high electron saturation velocity and a wide direct bandgap. Among the various GaN-based PDs, metal-semiconductor-metal ͑MSM͒ PD has attracted much attention due to its fabrication simplicity, low intrinsic capacitance, high operation speed, and low noise. 1-3 However, leakage current in GaN-based MSM-PDs is large because high dislocation density exists in GaN-based epitaxial layers prepared on sapphire substrate in general. 4 To solve this problem, one can insert an insulating layer between a metal and the underneath semiconductor. 5 For such metal-insulator-semiconductor ͑MIS͒ PDs, quality of the inserted insulator plays a very important role. GaN-based MIS PDs with various insulator materials, such as Al 2 O 3 , Ga 2 O 3 , SiO 2 , and insulator multilayer stacks, have all been reported. 6-13 Liquid phase deposition ͑LPD͒ is a reliable method to grow SiO 2 film on various semiconductor materials. Compared with other deposition methods, LPD SiO 2 film can be grown at a low temperature at an atmospheric pressure with low cost. The selective growth of the LPD SiO 2 film with a good step coverage is also possible.To further reduce leakage current in MIS PDs, we need to achieve a clean insulator/semiconductor interface. However, it is difficult to completely remove the native oxide on the surface of III-V compound semiconductors by standard cleaning methods. As a result, the high density of interface states is often observed in III-V compound semiconductor-based MIS devices. These interfacial states could cause the pinning of the surface Fermi level near the middle of the energy gap for the III-V MIS field effect transistors. These interfacial states could also result in a large leakage current in the III-V MIS PDs. It has been shown previously that ͑NH 4 ͒ 2 S x ͑S͒-treatment can prevent InP from oxidizing after cleaning. 14 Also, chemically bonded In-S species can be formed on the InP surface to assist the top InP layer in reconstructing its crystalline structure. Also, S-treatment can effectively passivate the surface of the AlInP window layer and thus enhance the conversion efficiency of III-V multijunction solar cells. 15 S-treatment also has a significant effect on GaN. Using X-ray photoelectron spectroscopy ͑XPS͒, Lin et al. found that nati...