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.
Integrated polarization focal plane detection imaging has the advantages of small size, high system integration, high mechanical stability and real-time polarization imaging in multiple polarization directions. We have developed a simulation model for back-illuminated mid-wave InAs/GaSb Type-II superlattices (T2SLs) infrared focal plane arrays (FPAs) on-chip integrated polarization grating. The polarization grating is an Al-ZnS double-layer subwavelength grating with antireflection coating, which has a better polarization transmission than a single-layer Al grating with the same deep slot. The effect of different grating parameters on the detector is simulated and optimized by the finite-difference time-domain (FDTD) method, and the results obtained are qualitatively interpreted in a physical sense by the Fabry-Perot-like (F-P-like) resonance theory. The optimized grating has a TM polarization transmittance higher than 92% and extinction ratios greater than 32 dB for wavelengths from 3-5 μm, and is suitable for infrared polarization imaging in the 0°-50° field-of-view range. The simulation results can provide theoretical basis and guidance for the design of polarization gratings for mid-infrared monolithic integrated polarization InAs/GaSb T2SLs FPAs.
SnTe is a new two-dimensional (2D) material, which has many merits, such as the bandgap of SnTe film can be adjusted by changing the film thickness hence its photoelectric properties can be regulated. SnTe belongs to topological crystal insulator (TCI) and has gapless topological surface states as well as exhibiting high carrier mobility at room temperature. SnTe has a narrow band gap and has potential for wavelength extension in the development of novel infrared photodetectors. Si is a traditional semiconductor material and has been widely used in the preparation of various semiconductor devices due to its numerous merits, such as low-cost and well-established preparation methodology. However, the detection wavelength of Si photoelectric detector is limited by its relatively large bandgap (1.12 eV). Recently, some progress has been made in fabricating photovoltaic detectors consisting of new 2D materials and Si. In this study, an efficient and low-cost magnetron sputtering method was used to prepare SnTe nanofilm on Si substrate. A photovoltaic detector based on the vertical heterostructure of SnTe/Si was fabricated using Al as electrode material. J-V characterization of the SnTe/Si heterostructure showed that the device exhibited good diode and photovoltaic characteristics under the illumination of various LED light sources with wavelength between 400 and 1450 nm, and its photocurrent was larger than the dark current. Moreover, under 850 nm illumination, the SnTe/Si device has a high responsivity (R) of 260 mA/W and detectivity (D*) of 3.36×1010 cmHz1/2W-1. Therefore, the device demonstrated potential application in the field of broadband photoelectric detection.
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.
The long-wave InAs/GaSb type II superlattice graded barrier structure was grown by MBE and applied to fabricate the various area diodes. The anodic sulfidization treatment, SiO2 film deposited by inductively coupled plasma chemical vapor deposition (ICP-CVD) and ion beam deposition (IBD) were combined into three methods to passivate the diodes. The variation of dark current density and the forming mechanism as related to diode sizes and measurement temperature was characterized and analyzed. The anodic sulfidization and IBD treated diodes show the worst dark current. The two groups of diodes passivated by anodic sulfidization and ICP-CVD obtained the lowest surface leakage current 3.74×10-5 A/cm2 and 5.08×10-5 A/cm2, the maximal surface resistivity 4.48×105 Ω·cm2 and 9.68×105 Ω·cm2 respectively.
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.
As a topological crystal insulator, tin telluride (SnTe) has unique properties that are different from those of traditional topological insulators. Due to its helical multi-surface states, strong topological protection characteristics, gapless topological surface states, narrow bulk band gap, high mobility at room temperature and other excellent properties, SnTe has a great application potential in photodetectors with minimal energy consumption, broad spectrum and ultra-fast response. However, the preparation of large area high quality SnTe nanofilms is still a big challenge. Here, we report a facile and efficient preparation method for large area SnTe nanofilm (2 cm ×2 cm) by RF magnetron sputtering method. The nanofilm having a thickness of 5.8 nm and surface roughness of 0.51 nm was obtained. Moreover, the prepared nanofilm was crystallized without annealing treatment and exhibited uniform surface. The photoconductive prototype device based on the SnTe nanofilm demonstrated a significant photoelectric response under an illumination of 365, 555 and 850 nm light source at room temperature. Furthermore, the ultraviolet, visible and near infrared photoelectric performance of the device remained stable even after six months in the atmosphere of the drying cabinet. These results indicate that the SnTe nanofilm has potential applications in broad spectrum photodetectors.
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