Semiconductor surface passivation

We have used spectroscopic ellipsometry to determine the complex dielectric function from 1.5 to 6.0 eV for Hg0.71Cd0.29Te and some of its native oxides. The electrochemically grown anodic oxide was found to have an absorption threshold near 3 eV and its dielectric function shows some of the features of TeO2. We found no evidence for a Te‐rich layer between the native oxide and the semiconductor. However, after stripping the oxide with HCl, a residual layer with Te‐like optical and chemical properties did appear. Thin native oxides formed by exposure to ozone‐containing oxygen had dielectric functions similar to that of the anodic oxide but with a broader absorption edge. These oxides could be stripped partly by water and totally by HCl. This confirms that they are a mixture of several oxides as also concluded in other investigations. We found no evidence for any disorder or defects induced in HgCdTe by anodization or etching.

Properties of Hg0.71Cd0.29Te and some native oxides by spectroscopic ellipsometry

Planar n/sup +/p Hg/sub 1-x/ Cd/sub x/Te (x=0.23) photodiodes passivated with ZnS were irradiated by a Co/sup 60/ gamma source. A strong increase in the reverse dark current was observed for doses above 0.3 Mrad(air). A similar effect is found by exposing the photodiodes to UV illumination from a high-pressure mercury lamp. By filtering the UV light it is shown that the degradation in the performance of the photodiodes is caused by the light or radiation absorbed in the ZnS layer above the implanted n-type region. C-V measurements of irradiated MIS devices showed a significant increase in the fast surface state density. Galvanomagnetic and lifetime measurements made on irradiated p-type HgCdTe layer showed no significant changes in the bulk transport parameters. Based on these findings, a model for the degradation mechanism is proposed. >

Degradation mechanisms of gamma irradiated LWIR HgCdTe photovoltaic detectors

High magnetic field characterisation of (Hg, Cd)Te surface layers

Electroreflectance from Hg1−xCdxTe in the metal‐insulator‐semiconductor configuration at 77 K as a function of gate voltage has been investigated. We find the spectra consist of contributions from two considerably different compositions, one of which corresponds to semimetallic material (x≊0.1). The x≊0.1 component is a consequence of the passivation of the HgCdTe surface. There is some evidence that these two regions are distributed across the surface rather than in depth. In addition, the two components have different responses to the gate voltage. The higher composition region can be driven through a flat band while the lower composition portion cannot.

Electroreflectance study of HgCdTe in the metal‐insulator‐semiconductor configuration at 77 K

This paper reports the effects of visible light and applied electric field on the properties of the HgCdTe–anodic oxide interface. The surfaces of anodized n‐type crystals are accumulated with a fixed positive charge in the oxide on the order of 5×1011 cm−2. However, illumination with photons of energy ?2.2 eV can neutralize and even invert these surfaces. The original surface charge is restored by placing the sample in the dark for periods of minutes at room temperature and weeks at 77 K. Based on our measurement of the oxide energy gap of 3.4 eV, the photo‐induced surface charging is attributed to internal photoemission of electrons from the HgCdTe valence band to the oxide conduction band. These photoemitted electrons fall into deep traps in the oxide and neutralize the fixed positive charge. When stored in the dark, these trapped electrons are thermally excited from the traps and recombined in the semiconductor. Charge exchange between the oxide traps and semiconductor can also be promoted by applying...

A. A. Fote

Papers

Optical and field effect studies of the Hg0.7Cd0.3 Te–anodic oxide interface