Use of epitaxial gallium arsenide in detectors

Abstract

The results of investigations of semiconductor detectors on the basis of epitaxial layers of gallium arsenide for detecting x rays and low-energy radiation are examined. It is shown that epitaxial layers ranging in thickness from 60 to 300 µm with current carrier density ≤5·10 13 cm −3 and electron mobility ≥6000 cm 2 /(V·sec) at 300 K hold promise for such detectors.A new type of photovoltaic x-ray detector based on the epitaxial structures p + -n-n i -n + GaAs is described. Such detectors possess high charge collection efficiency with zero bias at room temperature and can operate in two regimes -counting and current integration -and will substantially expand the dynamical range of image formation when used in scanning systems.Gallium arsenide was chosen as a basis for developing non-cooled semiconductor detectors with different possibilities. The low resolution and high noise in the first semiconductor detectors based on GaAs were due to be high defect density in and contamination of bulk crystals, grown from melt, with impurities. Experiments show that there is a definite threshold of their structural and electrophysical perfection which cannot be overcome using the indicated technology. Epitaxial technology has made it possible to overcome the limitations due to crystal growth from melt and to obtain detector-quality material [1].The methods of liquid-and gas-phase epitaxy are used to obtain detector-quality GaAs. In the present work, we report on investigations of experimental samples of detectors based on epitaxial layers of GaAs grown in the system Ga-AsCl 3 -H 2 [2]. Their characteristics are presented in Table 1.Using initial materials of the highest purity and optimizing the process conditions, including control of the behavior of background impurities, has made it possible to obtain consistently n-type epitaxial layers of GaAs with carrier density ≤10 14 cm −3 and electron mobility ≥7000 cm 2 /(V·sec) at 300 K. The thickness of the layers ranged from 60 to 300 µm. They were used as a basis to fabricate several tens of detector structures for spectrometry of x-rays and gamma rays at 300 K. The detector structure consisted of a surface-barrier diode in which a n-n + junction is produced by growing a pure epitaxial layer (n) on a strongly doped substrate (n + ) and a barrier is produced by depositing gold on the epitaxial surface. The gold film was 20 ± 5 nm thick, the area was 3-5 mm 2 , and the leakage current wireless 2·10 -8 A with a bias voltage of 200 V. The absolute efficiency of the detectors based on GaAs with 100-200 µm thick sensitive region reached 15-28% for photon energy 14 keV and decreased to 3-8% for 60 keV. The efficiency is only ~2% on the 122 keV line. The efficiency of detectors drops sharply outside this range.

Atomic spectrometry update. X-ray fluorescence spectrometry

“…Such advice should be headed and is normally included as part of the set up of most EDXRF systems, irrespective of the detector material. Although interest continued in GaAs detectors during the review period, [25][26][27] these papers were limited to the fabrication and use of GaAs for X-ray 2D imaging detectors where the stopping power of the GaAs is an advantage but there was no use made of the potential energy dispersive detection from the devices. The potential of diamond as a detector material was reported by De Sio et al, 28 whose focus was mainly on photon counting and extreme radiation hardness in high energy physics and SR applications rather than as useful energy dispersive detectors.…”