Development of AlGaAs avalanche diodes for soft X-ray photon counting

Abstract

We report on the performance of avalanche photodiodes (APDs) based on the wide band gap material AIGaAs which have been developed for soft X-ray spectroscopy applications. A number of diode types with different layer thicknesses have been characterised. The temperature dependence of the avalanche multiplication process at soft X-ray energies in Alo.sGao.zAs APDs was investigated at temperatures from +80 °C to -20°C. X-ray spectra from a 55 Fe radioactive source show these diodes can be used for spectroscopy with promising energy resolution (0.9-2.5keV) over a wide temperature range. The temperature dependence of the pure electron initiated multiplication factor (Me) and the mixed carrier initiated avalanche multiplication factor (MmO> were experimentally measured. The experimental results are compared with a spectroscopic Monte Carlo model for Alo.sGao.zAs diodes from which the temperature dependence of the pure hole initiated multiplication factor (Mh) is determined.AlxG3.x_1As has received attention as a potentially desirable material from which to fabricate soft X -ray spectroscopic photon counting photodiodes [1-9]. In particular, Alo.sGao.2As X-ray photon counting spectroscopic p+-i-n+ photodiodes have been shown to operate in avalanche mode over a wide temperature range (-30 to +90°C) [4][5][6][7][8]. For Alo.2Gao.sAs [4], Alo.4Gao. 6 As [4] and Alo.sGao.2As [5], the electric field dependence of the electron and hole impact ionization coefficients have been reported. However, the temperature dependence of the impact ionization coefficients has not receive the same amount of attention with a limited number of reports appearing in the literature for Alo.2Gao.sAs and Alo.4Gao. 6 As [4] and more recently Alo.sGao.2As [6].In this paper we show that the ionization coefficients can be extracted from measurement of the X -ray spectra as a function of bias voltage. We also report the temperature dependence of the avalanche multiplication process at a typical operating electric field in Alo.sGao.2As p+-p--n+ spectroscopic X-ray photon counting APDs. The temperature dependence of the electron and hole ionization coefficients is derived and shown. II. DIODE DESIGN AND CHARACTERISTICSThe wafer used in this study is an Alo.sGao.2As p+-p--n+ diode grown on an n+ (100) on-axis GaAs substrate (thickness of 350 flm) by a VG V80 Molecular Beam Epitaxy (MBE) machine. The fabricated diodes were unpassivated mesa APDs with radii of 25 flm, 50 /lm, 100 /lm and 200 /lm. Further details of the diode fabrication and wafer growth can be found in [4]. The major epitaxial layer material thicknesses and deduced doping densities are given in Table 1. Although the wafer was originally intended to be an Alo.sGao.2As p+-i-n+ diode, doping information deduced from devices fabricated from the wafer indicate that that the structure resembles a p + P --n + diode. TABLE I. DIODE LAYER PARAMETERS Layer Material Thickness (J.Lm) Type Na 1 AlGaAs 0.92 P 4xlO " 2 AlGaAs 0.58 P 5xlO l6 2 AlGaAs 1.0 N 2xlO I8 III. EXPERIMENTAL METHODThe diodes were co...

Analysis of I–V-T characteristics of Be-doped AlGaAs Schottky diodes grown on (100) GaAs substrates by molecular beam epitaxy

“…As seen in Fig. (9), 𝑅 𝑆 values increase with decreasing temperature. As temperature decreases, 𝑅 𝑆 values determined using Cheung's method are, closer to those determined using the standard method, whereas 𝑅 𝑆 values extracted using Norde's method exhibit higher values.…”

“…Aluminium Gallium Arsenide (AlxGa1−xAs), which is lattice matched to GaAs, has a larger bandgap than GaAs and is widely used as an active material in many heterostructures for a wide range of device applications, such as high electron mobility transistors [6], lasers [7], particle detectors [8] and Schottky barrier diodes (SBDs) [9,10]. SBD is a metal-semiconductor (MS) contact that exhibits a rectified current-voltage (𝐼 − 𝑉) characteristic.…”