Metal-organic vapor-phase epitaxy growth and characterization of thick (100) CdTe layers on (100) GaAs and (100) GaAs/Si substrates

Uchida

et al. 2004

phys. stat. sol. (c)

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PACS 78.55.Et, 81.05.Dz, 81.15.Gh, 85.60 .GzThe heteroepitaxial growth and characteristics of thick CdTe layers of thickness up to 200 µm grown on GaAs substrates in an atmospheric pressure MOVPE growth system are reported. The X-ray double crystal rocking curve analysis showed the crystalline quality of the epitaxial layers was high, the full width at half maximum values of the CdTe (400) diffraction peaks was around 50-70 arcsec for the layers thicker than 30 µm. Photoluminescence measurements at 4.2 K showed high-intensity bound excitonic emissions and very small defect related peaks indicating their superior structural properties. Surface morphology of the layers was highly dependent on the growth process, and was improved by adopting a two-step growth technique, where a buffer layer was grown first at a low substrate temperature followed by the usual high temperature growth.

Section: Resultsmentioning

confidence: 60%

MOVPE growth of thick CdTe heteroepitaxial layers for X‐ray imaging detectors

Uchida

et al. 2004

phys. stat. sol. (c)

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“…6 In this work, we further report on even thicker layers of thickness, up to 200 µm, by the same growth technique and explain how high resistivity layers of superior quality were obtained. We further evaluate a heterojunction diode fabricated by growing CdTe layers on an n ϩ -GaAs substrate for its application in an x-ray imaging device.…”

Section: Introductionmentioning

confidence: 70%

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

Nakanishi

et al. 2004

Journal of Elec Materi

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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.

“…These detectors have superior charge transport properties, as evident from the TOF and the nuclear radiation measurement, in comparison to our previous detectors where no buffer layers or undoped CdTe buffer layers were used. 12,13 In our previous detectors, no clear TOF signal and no information on the charge transport property was available. Likewise, no any information was obtained from the nuclear radiation measurements.…”

Section: Resultsmentioning

confidence: 99%

“…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 .…”

Section: Detector Fabricationmentioning

confidence: 99%

“…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.…”

Section: Introductionmentioning

confidence: 99%

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

Takagi

et al. 2005

Journal of Elec Materi

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A CdTe/n ϩ -GaAs heterojunction diode for a room-temperature nuclear radiation detector has been developed and demonstrated. The heterojunction diode was fabricated by growing a 2-5-µm-thick iodine-doped n-CdTe buffer layer on the n ϩ -GaAs substrates, followed by about 100-µm-thick undoped p-like single crystalline CdTe layer using metalorganic vapor-phase epitaxy. The n-type buffer layer was found to be essential to improve the junction property of the diode detector. The diode detectors exhibited good rectification property and had the reverse leakage currents typically from 1 µA/cm 2 to 5 µA/cm 2 at 40 V bias. The detector clearly demonstrated its energy resolution capability by resolving the 59.54-keV gamma peak from the 241 Am radioisotope during the radiation detection test.