SI-GaAs detectors with epitaxial junction (original) (raw)
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Evidence for charge gain mechanism in SI-GaAs detectors with epitaxial junction
IEEE Transactions on Nuclear Science, 2000
We made a characterisation of GaAs detectors with an epitaxial p-type layer deposited on the 200 pm semi-insulating substrate. The charge collection efficiency for 60-keV photons and 5.49 MeV alpha particle depends on the doping level of the player. When completely depleted (reverse bias > 200-300 V), the collected charge can be greater than 100 %, implying the presence of some charge gain mechanism. At the same reverse bias and doping concentration, the collected charge depends also on the size of the contact pad. Moreover, the lower the p-doping, the lower the current density. The present findings confirm our previous work, obtaining gains up to 4: 1.
Journal of Applied Physics, 1994
The performance of Schottky contact semiconductor radiation detectors fabricated from semi-insulating GaAs is highly sensitive to charged impurities and defects in the material. The observed behavior of semi-insulating GaAs Schottky barrier alpha particle detectors does not match well with models that treat the semi-insulating material as either perfectly intrinsic or as material with deep donors (EL2) of constant capture cross section compensated with shallow acceptors. We propose an explanation for the discrepancy based on enhanced capture of electrons by EL2 centers at high electric fields and the resulting formation of a quasineutral region in the GaAs. Presented is a simple model including field enhanced electron capture which shows good agreement with experimental alpha particle pulse height measurements. 7910
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1999
It is generally agreed that the substrate material quality plays a key role in the performance of back-to-back detectors of ionising radiation based on semi-insulating (SI) material. The aim of this paper is to evaluate usually overlooked problem, namely the influence of the Schottky contact preparation on detector performance. We report on different approaches to modify and control the quality of the metal/SI GaAs interface via a treatment of the SI-GaAs surface by means of low-temperature hydrogen plasma and wet etching. The measured electrical and detecting properties of such structures display a strong dependence on the history and the way the GaAs surface is treated prior to the metal evaporation. We point out, therefore, that the semiconductor surface treatment before the Schottky metallization plays a role of comparable importance to the influence of the SI-GaAs substrate properties on detector performances.
Simulation of Semiconductor Processes and Devices 2001, 2001
In the present work we have conducted theoretical calculations of the transient response of SI GaAs radiation detectors. The detector under consideration is a typical reverse biased Schottky diode of high purity undopped GaAs or compensated material. The electrical characteristics of the "dark" equilibrium state, derived by the Poisson and continuity equations, indicate that in the compensated detector is established a wider active region [I]. We considered that the detector operates in pulse or current mode. In pulse mode, a single charged particle (i.e. proton, a-particle) incidents the detector on either the Schottky or ohmic contact, whereas in current mode the detector is irradiated by a short-lived particle beam.
A study of the electrical and charge-collection properties of semi-insulating GaAs detectors
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1996
In this work a numerical approach has been used to investigate some properties of semi-insulating GaAs detectors. In particular, the electric field and the carriers mean free path distributions have been obtained, by solving transport and Poisson equations. The knowledge of these quantities allows us to determine the ch~ge-collection efficiency and other detector characteristics. A comparison with the experimental results of X-ray irradiated detectors of different thicknesses has been carried out.
Detection properties of LEC SI GaAs radiation detectors with the symmetrical contact configuration
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1996
1-V characteristics and detection properties (CCE, FWHM) of the semi-insulating GaAs detectors (base length 200 txm) with the Au-Au and W-W Schottky barriers and N+-N + ohmic contacts, measured at room temperature, are presented for o<, ,8 and heavier particles (up to Z-~ 10). The best results (average values of CCE and FWHM were 87% and 5%, respectively, for 5.48 MeV a particles from 24~Am) give detectors with the Au-Au contact configuration. Detectors with the N + contacts have worse parameters, about 30% for both, the CCE and FWHM, respectively. Nevertheless, such detectors operate at a low bias voltage, under 20 V.
On the spectrometric performance limit of radiation detectors based on semi-insulating GaAs
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2004
In this work, basic tasks related to the spectrometric performance of X-and gray radiation-imaging detectors based on semi-insulating (SI) GaAs are studied. The state of the art in this field is reported. The importance of a low-noise front-end read-out electronic chain is demonstrated. Four different charge-sensitive preamplifiers are tested and compared. The investigation of SI GaAs detectors considered for imaging applications is focused on the study of different electrode technologies. A blocking electrode is obtained by a surface Schottky barrier or an MBE-grown P + layer. An ohmic N + contact is fabricated using alloyed AuGeNi metallization or an advanced, quasi-ohmic noninjecting system created by a non-stoichiometric buffer grown by low-temperature MBE at the metal-semiconductor interface. This latter approach is considered as an improvement of the ''non-alloyed'' ohmic contact. The pulse height spectra obtained with 241 Am and 57 Co sources and corresponding detector energy resolution are evaluated. The role of detector geometry and temperature on the spectrometric performance is studied.
Influence of electron traps on charge-collection efficiency in GaAs radiation detectors
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1994
This paper deals with the interpretation of the charge-collection efficiency for minimum ionizing particles in terms of electron traps in semi-insulating liquid encapsulated Czochralski gallium arsenide detectors fabricated with thicknesses of 80 µm, 200 µm, and 300 µm. The results, obtained within the context of the RD-8 project, show that low values of chargecollection efficiency cannot be ascribed primarily to the presence of high concentrations of EL2 defects. Possible ways of increasing the charge-collection efficiency are briefly addressed.