KEYWORDS: Dark current, Sensors, Infrared detectors, Long wavelength infrared, Black bodies, Activation energy, Temperature metrology, Superlattices, Laser sintering, Gallium antimonide
Advances in bandgap engineering of various III-V compound semiconductors have led to innovative infrared detector architectures such as InAs/GaSb barrier-type structures. This barrier-type structure detectors are characterized by enhanced carrier transport optimization, a significant reduction in interface state density, and superior thermal stability, alongside a notable reduction in dark current and noise levels. These improvements not only substantially enhance the fundamental electrical characteristics of semiconductor devices but also expand their application flexibility and environmental adaptability through meticulous bandgap engineering. This article reports a study on optoelectronic properties based on a graded barrier InAs/GaSb T2SLs long-wave infrared detector for the first time, with detailed analysis from two aspects: electrical and optical properties. The surface leakage current is measured through variable area testing. The study correlates effective bandgap and activation energy across temperatures, providing insights into bulk dark current components. In addition, the temperature dependence of blackbody responsivity is also analyzed.
HgCdTe films grown by Molecular Beam Epitaxy (MBE) are essential for creating high-performance Infrared Focal Plane Arrays (IRFPAs) like dual band detectors, High Operating Temperature (HOT) detectors, and Avalanche Photodiode (APD) detectors. CdZnTe is recognized as the optimal substrates for growing high crystal quality HgCdTe due to its lattice matching, which is adjusted by selecting the Zn mole fraction. If the Zn mole fraction in CdZnTe substrates falls outside the ideal range, it may lead to an increase in dislocation density in HgCdTe films, thereby adversely affecting the performance of the device. A proposed method has been introduced for designing a lattice-matching buffer layer between CdZnTe substrates and HgCdTe films. Growth of HgCdTe on CdZnTe substrates with an unsuitable Zn mole fraction was conducted with and without a lattice-matching buffer layer. Results showed that the dislocation density of the HgCdTe film obtained on CdZnTe substrates with an unsuitable Zn mole fraction usually exceeds 1×106 cm-2. However, as expected, the presence of a lattice-matching buffer layer significantly reduced the dislocation density of HgCdTe films. The dislocation density can be effectively controlled within 3×105 cm-2, with a mean value around 1×105 cm-2 . By doing so, the allowable range of Zn mole fraction in substrates for producing high-quality HgCdTe films can be widened, which holds significant engineering implications for the manufacturing of MBE HgCdTe.
Non-equilibrium photovoltaic HgCdTe detector with a P+ νN+ structure has been demonstrated to work at high temperature, in which carriers were swept out in a non-equilibrium condition, resulting in a significant decrease of carrier concentration. The P+ -type layer grown by Molecular Beam Epitaxy (MBE) is achieved by arsenic (As) doping, followed by high temperature annealing to activate As. However, due to the annealing temperature is higher than 400 °C, interdiffusion of cations (cadmium (Cd) ion and mercury (Hg) ion) can easily take place in such a high temperature, leading to a higher Cd component and shorter absorption region in the absorber layer, which can ultimately decrease the optical absorption and quantum efficiency of the device. Herein, we proposed a P+G4G3νG2G1N+ heterostructure, which can effectively trap the Cd ions diffusing from the P+ and N+ regions due to the component low-lying area between G4G3 and G2G1. In this work, we firstly investigated the performance using Silvaco, the simulation results indicated that this P+G4G3νG2G1N+ heterostructure can effectively achieve Auger suppression at 200K. High quality and uniform HgCdTe epilayers on CdZnTe substrate were fabricated. The effective thickness of the absorption layer after annealing reduced by more than 1.5 μm due to interdiffusion of the Cd ions in a conventional P+ νN+ structure. In sharp contrast, the effective thickness of the absorption layer after annealing reduced within 0.5 μm in the as-designed P+G4G3νG2G1N+, indicating an inspired way to fabricate high performance HOT non-equilibrium HgCdTe detector.
Long-wavelength infrared InAs/GaSb type-II superlattice PπBN photodetectors are demonstrated on GaSb substrates. The focal plane array device consists of a 2.0μm thick absorber layer and has a 50% cutoff wavelength of 11.3μm, and a maximum resistance-area product of 800 Ω•cm2 at 77 K. And the resistance-area product stay above 500 Ω•cm2 at the range from -200 mV to -1100 mV. These single units show good consistency. It has laid a reliable foundation for the manufacturing of focal plane arrays.
In this article, the band structures of InAs/InAsSb superlattices are calculated by sp3s* model, which is based on empirical tight-bonding method (ETBM). First, the band structures of InAs/InAsSb superlattice with varies period are calculated, the calculated bandgap results are consistent with experiment values. The conduction band edge (Ec level) for the two sets of InAs/InAsSb T2SLs are approximately independent of the cutoff wavelength (or band gap), and they are significantly lower than the conduction band edges of InAs/GaSb. The relationship between periodic structure and cutoff wavelength is obtained under the condition of strain balance. Then the holes effective mass at Γ point of mini-band along the growth direction for different structure InAs/InAsSb superlattice are derived. Finally, the composition segregation function is included in our model in order to study the impact of Sb segregation on InAs/InAsSb superlattice. These material parameters obtained from our calculated results can be used in the design of T2SL-based IR detectors.
HgCdTe films with low defect density grown by molecular beam epitaxy(MBE) has been proved to be irreplaceable materials for fabricating high performance infrared focal plane arrays(IRFPAs) such as dual band detector, high operating temperature(HOT) detector and avalanche photodiode(APD) detector. CdZnTe is the best choice of substrates for epitaxy of HgCdTe owning to the perfectly matched lattice. However, the Cd-rich or Te-rich precipitates in CdZnTe substrates are hard to completely eliminate. These precipitates in the CdZnTe substrates induced the formation of precipitate-related defects at the HgCdTe layer, resulting in detrimental device performance, especially for detectors with small pixel size and high operability. To understand the origin of the precipitate-related defects at the HgCdTe layer, we investigated the influences of Cd-rich and Te-rich precipitates in CdZnTe substrates on dislocations and macro-defects in HgCdTe gown by MBE. Gridlines were produced by photolithographic and wet etching process to locate small defects in SEM according to the location in dark field microscopy. Results indicated that Cd-rich precipitate leads to formation of a dislocation cluster in HgCdTe film. Etch pit density(EPD) in dislocation cluster area is in the range of 2×106 to 6×106 cm-2, about one to two orders of magnitude larger than EPD in a normal region. EPD in the cluster varies with depth of Cd-rich precipitates, and the relationship between them accords well with 1/h dislocation fall-off law, suggesting a minimum EPD of 5×105 cm-2 in dislocation cluster. In contrast, no dislocation cluster was found in HgCdTe film on CdZnTe with Te-rich precipitates, but Te-rich precipitates can lead to macro-defects, even under the optimum growth conditions. The typical macro-defect density resulted from Te-rich precipitates of state-of-the-art HgCdTe/CdZnTe is range from 100 to 500 cm-2, which is considered limited by Te-rich precipitates with size of 100 to 1000 nm if the high-density macro-defects caused by particles or pollution residues on CdZnTe substrates are excluded.
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