Surface treatment effects on the electrical properties of insulator/HgCdTe interface

Abstract

Two subjects have been studied in this thesis. The one is about the surface treatment effects and the other is the effect of fixed charges and overlap metal on the I-V characteristics of HgCdTe photodiodes. At first, a new simple surface treatment method is proposed, which is a kind of post-etch treatment composed of chemical oxidation of HgCdTe with $HNO_3$ and removal of the oxide with $NH_4OH$. Since strong $HNO_3$ is used, the new method can make the HgCdTe surface cleaner than the conventional method of KAIST. Even though the HgCdTe surface is roughened by Br-MeOH etch, the surface can be made smoother with the new method, which is observed using atomic force microscopy (AFM). In applications to the MIS capacitors, the new surface treatment resulted in reproducible improvements in capacitance-voltage (C-V) characteristics such as low fixed charge and slow surface state densities. These improvements are thought to result from some aspects of the new method. One is the surface smoothing function of the new surface treatment. The other is that the non-stoichiometric surface layer of the HgCdTe caused by Br-MeOH etch may be consumed by the chemical oxidation and then removed together with the oxide. However, it was found that much more dilute chemicals should be used for LPE-grown HgCdTe wafers than for bulk ones. Otherwise, the CdTe substrates of the LPE wafers were seriously attacked. In chapter III, the effects of bromine etch and dilute HNO3 post-etch treatment on the C-V characteristics of MIS devices with ZnS on LPE-grown HgCdTe wafers have been studied. C-V characteristics of most devices at 1 MHz showed more increased surface doping concentrations than the original values of the wafers, and these apparent doping concentrations were dependent on the surface treatments. These are thought to result from the surface treatment effects on the interface trap density and the surface minority carrier response time (tR). It was found the interface trap density...