Energy‐Sensitive GaSb/AlAsSb Separate Absorption and Multiplication Avalanche Photodiodes for X‐Ray and Gamma‐Ray Detection

Abstract

and multiplication avalanche photodiodes (SAM-APDs) composed of photoabsorbers and large bandgap multiplication regions are advantageous for achieving highefficient and low-noise photodetection with high-energy resolution. [11][12][13] Such a detector architecture can be also applied to energy-sensitive gamma-ray and X-ray detection. A GaAs/AlGaAs SAM-APD comprised of a 4.5 µm absorption region and a staircase-like multiplication region has been developed for X-ray photodetection. [14] Meanwhile, a similar GaAs/ Al 0.8 Ga 0.2 As SAM-APD structure has been also demonstrated to detect soft X-rays at 5.9 keV with a full-width half-maximum (FWHM) of 1.08 keV. [15] However, its spectroscopic characterizations show an undesired secondary peak located at energy lower than the 5.9 keV peak. This is because of 1) different degrees of impact ionization experienced by the electrons and holes; [16][17][18] 2) insufficient layer thickness ratio; [19] and 3) inadequate difference of pair creation energy (PCE) between GaAs and AlGaAs. [20,21] Indeed, the absorption efficiency can be improved by simply increasing the thickness of the absorption layer. Unfortunately, the commonly used (Al)GaAs semiconductors are not able to concurrently offer high-Z (i.e., high atomic number) absorption and large PCE difference within SAM structures for highenergy X-ray or gamma-ray detection.Alternatively, the antimony-based (Sb-based) SAM-APD structure with high-Z GaSb and large bandgap AlAsSb is promising. GaSb absorbers can provide a much higher probability than GaAs to stop X-ray and gamma-ray photons at a given energy due to a relatively higher Z. [22] In addition, the GaSb/AlAsSb material system provides a larger dissimilarity in both PCE and absorption efficiency. [23,24] This allows for a significant suppression of spurious photopeaks, which are generated outside the intended absorption regions. The combination of these unique capabilities shows promise for achieving X-ray and gamma-ray detectors with high spectroscopic performance. To prove the concept, we develop GaSb/AlAsSb SAM-APDs composed of 2 µm GaSb absorbers and AlAsSb digital alloy multiplication regions to detect X-ray and gamma-ray photopeaks under irradiation from 241 Am sources. Due to the reduced high-peak electric Demonstrated are antimony-based (Sb-based) separate absorption and multiplication avalanche photodiodes (SAM-APDs) for X-ray and gamma-ray detection, which are composed of GaSb absorbers and large bandgap AlAsSb multiplication regions in order to enhance the probability of stopping highenergy photons while drastically suppressing the minority carrier diffusion. Well-defined X-ray and gamma-ray photopeaks are observed under exposure to 241 Am radioactive sources, demonstrating the desirable energy-sensitive detector performance. Spectroscopic characterizations show a significant improvement of measured energy resolution due to reduced high-peak electric field in the absorbers and suppressed nonradiative recombination on surfaces. Additionally, the GaSb/AlAsSb SAM...

Significant suppression of surface leakage in GaSb/AlAsSb heterostructure with Al2O3 passivation

“…Such heterostructures are based on our previously studied GaSb/AlAsSb separate absorption and multiplication avalanche photodiodes (SAM-APDs). 23) We observe a significant suppression of dark current at reverse bias, and a remarkable improvement of avalanche breakdown, both at room temperature. To understand the underlying physics, we further extract activation energies and breakdown temperature coefficients.…”

“…shown GaSb/AlGaSb SAM-APDs, i.e., the electric field is entirely confined in the large bandgap AlAsSb regions thanks to the SAM structure. 23) Conversely, if the breakdown event takes place in the small bandgap GaSb regions, an abrupt increment in dark current from BTBT would occur. In addition, the comparable Cbd regardless of the passivation treatment is likely due to the fact that Cbd is an intrinsic bulk characteristic and not affected by the surface conditions.…”

“…Such heterostructures were developed based on our previous study on GaSb PIN diodes and GaSb/AlAsSb SAM-APDs for energy-sensitive photodetection, along with a series of detector characterizations, which include current-voltage (I-V ), capacitance-voltage (C-V ), photo-response, radiation response, among others. 18,[23][24][25] The AlAsSb region was lattice-matched to the GaSb region, grown by molecular beam epitaxy (MBE) on an n-type GaSb substrate. 23,25) Tellurium and Beryllium were used as n-type and p-type dopants, respectively.…”

“…18,[23][24][25] The AlAsSb region was lattice-matched to the GaSb region, grown by molecular beam epitaxy (MBE) on an n-type GaSb substrate. 23,25) Tellurium and Beryllium were used as n-type and p-type dopants, respectively. The growth was started with the multiplication region.…”

Optimization of surface passivation for suppressing leakage current in GaSb PIN devices

“…The GaSb nanostructures are widely applied in photodetectors due to their high carrier mobility and bandgap engineering flexibility [1 ]. However, unpassivated GaSb devices are prone to high trap state density from unterminated dangling bonds and native oxides.…”