Growth of thick CdTe epilayers on GaAs substrates and evaluation of CdTe/n+-GaAs heterojunction diodes for an X-ray imaging detector

Abstract

The growth characteristics of thick (100) CdTe epitaxial layers of a thickness up to 200 µm on a (100) GaAs substrate in a metal-organic vapor-phase epitaxy (MOVPE) system and fabrication of CdTe/n ϩ -GaAs heterojunction diodes for their possible applications in low-energy x-ray imaging detectors are reported. The grown epilayers were of high structural quality as revealed from the x-ray double-crystal rocking curve (DCRC) analysis, where the full-width at half-maximum (FWHM) values of the (400) diffraction peaks was between 50 arcsec and 70 arcsec. The 4.2-K photoluminescence (PL) showed high-intensity bound-excitonic emission and very small defect-related peaks. The heterojunction diode fabricated had a good rectification property with a low value of reverse-bias current. The x-ray detection capability of the diode was examined by the time-of-flight (TOF) measurement, where good bias-dependent photoresponse was observed, but no carrier transport property could be deduced. It was found that the CdTe layer has a large number of trapping states as attributed to the cadmium-related vacancy and Ga-impurity, diffused from the substrate, related defect complexes.

Direct growth of high-quality thick CdTe epilayers on Si (211) substrates by metalorganic vapor phase epitaxy for nuclear radiation detection and imaging

“…[4][5][6] We have previously reported on the growth of CdTe layers on GaAs substrates and development of nuclear radiation detectors based on CdTe/n 1 -GaAs heterojunction diodes. 5,6 Although the nuclear radiation detection property of this heterojunction diode was successfully confirmed, in order to improve detector performance further and to achieve an even larger area, the Si substrate is considered to be more favorable than the GaAs substrates.…”

Development of nuclear radiation detectors based on epitaxially grown thick CdTe layers on n+-GaAs substrates

“…The details about the CdTe growth on the GaAs substrates and their characterization are reported elsewhere. [13][14][15] In order to improve the heterojunction property, a 2-5-µm-thick iodinedoped n-CdTe buffer layer was first grown at a low substrate temperature of 350°C, and was followed by the undoped p-like thick layer growth. The buffer layer has a room-temperature electron concentration of 10 16 -10 17 cm Ϫ3 .…”

“…We have previously reported on the successful growth of thick (up to 200 µm) and highquality CdTe epilayers on the GaAs substrates, and presented our efforts on detector development, which were based on CdTe/n ϩ -GaAs heterojunction diodes. 13,14 In spite of achieving a good diode property, the charge transport property of those diodes was rather poor, and it was not possible to obtain energy information of incident nuclear radiation. It was considered that the interface defect states at the junction as well as defect states in the CdTe layers possibly introduced due to the Ga diffusion were responsible for the poor transport property.…”

“…It was considered that the interface defect states at the junction as well as defect states in the CdTe layers possibly introduced due to the Ga diffusion were responsible for the poor transport property. 14 In order to overcome this problem, we introduced a low-temperature-grown iodine-doped buffer layer. It was found that this buffer layer is essential to improving the heterojunction property.…”

Optical emission characteristics of ablation plasma plumes during the laser-etching process of CdTe

“…Many studies on the detector fabrication have been reported in recent years. [1][2][3] One problem of the detector fabrication is formation of deep isolation trenches, which CdTe and HgCdTe pixel detectors require. In order to form deep isolation trenches, a high-speed etching technique is required.…”