Semiconductor Quantum Structures for Ultraviolet-to-Infrared Multi-Band Radiation Detection

In this work, multi-band (multi-color) detector structures considering different semiconductor device concepts and architectures are presented. Results on detectors operating in ultraviolet-to-infrared regions (UV-to-IR) are discussed. Multi-band detectors are based on quantum dot (QD) structures; which include quantum-dots-in-a-well (DWELL), tunneling quantum dot infrared photodetectors (T-QDIPs), and bi-layer quantum dot infrared photodetectors (Bi-QDIPs); and homo-/heterojunction interfacial workfunction internal photoemission (HIWIP/HEIWIP) structures. QD-based detectors show multi-color characteristics in mid- and far-infrared (MIR/FIR) regions, where as HIWIP/HEIWIP detectors show responses in UV or near-infrared (NIR) regions, and MIR-to-FIR regions. In DWELL structures, InAs QDs are placed in an InGaAs/GaAs quantum well (QW) to introduce photon induced electronic transitions from energy states in the QD to that in QW, leading to multi-color response peaks. One of the DWELL detectors shows response peaks at ∼ 6.25, ∼ 10.5 and ∼ 23.3 µm. In T-QDIP structures, photoexcited carriers are selectively collected from InGaAs QDs through resonant tunneling, while the dark current is blocked using AlGaAs/InGaAsAlGaAs/ blocking barriers placed in the structure. A two-color T-QDIP with photoresponse peaks at 6 and 17 µm operating at room temperature and a 6 THz detector operating at 150 K are presented. Bi-QDIPs consist of two layers of InAs QDs with different QD sizes. The detector exhibits three distinct peaks at 5.6, 8.0, and 23.0 µm. A typical HIWIP/HEIWIP detector structure consists of a single (or series of) doped emitter(s) and undoped barrier(s), which are placed between two highly doped contact layers. The dual-band response arises from interband transitions of carriers in the undoped barrier and intraband transitions in the doped emitter. Two HIWIP detectors, p-GaAs/GaAs and p-Si/Si, showing interband responses with wavelength thresholds at 0.82 and 1.05 µm, and intraband responses with zero response thresholds at 70 and 32 µm, respectively, are presented. HEIWIP detectors based on n-GaN/AlGaN show an interband response in the UV region and intraband response in the 2-14 µm region. A GaN/AlGaN detector structure consisting of three electrical contacts for separate UV and IR active regions is proposed for simultaneous measurements of the two components of the photocurrent generated by UV and IR radiation

Optical switching performance of thermally oxidized vanadium dioxide with an integrated thin film heater

Optical switching performance of vanadium dioxide produced by thermal oxidation of vanadium is presented in this paper. A 100nm thick vanadium was oxidized under controlled conditions in a quartz tube furnace to produce approximately 200nm thick VO2. The substrate was appropriately coated on the front and back side to reduce reflection in the cold state, and an integrated thin film heater was fabricated to allow in-situ thermal cycling. Electrical measurements show a greater than three orders of magnitude change in resistivity during the phase transition. Optical measurements exhibit 70% transparency at 1500nm and about 15dB extinction across a wide spectral band between 1000nm and 3000nm. These results are used to show a huge optical bistability effect in VO2-based devices

Photodetector Focal Plane Arrays Integrated with Silicon Micropyramidal Structures in MWIR

Light-concentrating truncated Si micropyramidal arrays with 54.7 degree sidewall angles were successfully integrated with PtSi Schottky barrier photodetectors. Four different devices consisting of 10 x 10 photodetectors with 60 um pitch combined in parallel were tested, where significant enhancement capability was demonstrated by the Si micropyramids. The device consisting of one hundred 22 um square detectors monolithically integrated with the light-concentrating micropyramidal array displayed signal enhancement of up to 4 times compared to the same size 22 um square photodetector device without the light concentrators.Comment: 4 pages, 2 figures, GOMACTech 202

Focusing and Diffraction of Light by Periodic Si Micropyramidal Arrays

This research was devoted to modeling of the optical properties of Si micropyramids aimed at designing optimal structures for applications as light concentrators in mid-wave infrared (MWIR) focal place arrays (FPAs). It is shown that completely different optical properties of such structures can be realized using two types of boundary conditions (BCs): i) periodical and ii) perfectly matched layer. The first type (periodical BC) allowed us to describe the Talbot effect under plane wave coherent illumination conditions. This effect was experimentally demonstrated in the proposed structures. The second type (perfectly matched layer BC) allows describing the optical properties of individual micropyramids concentrating or focusing light on the photodetector. The optimal geometries of micropyramids required for maximizing the intensity of photonic nanojets emerging from their truncated tips are determined.Comment: 4 pages, 5 figures, GOMACTech 202

Temperature-Dependent X-ray Diffraction Measurements of Infrared Superlattices Grown by MBE

Strained-layer superlattices (SLSs) are an active research topic in the molecular beam epitaxy (MBE) and infrared focal plane array communities. These structures undergo a >500 K temperature change between deposition and operation. As a result, the lattice constants of the substrate and superlattice are expected to change by approximately 0.3%, and at approximately the same rate. However, we present the first temperature-dependent X-ray diffraction (XRD) measurements of SLS material on GaSb and show that the superlattice does not contract in the same manner as the substrate. In both InAs/InAs0.65Sb0.35 and In0.8Ga0.2As/InAs0.65Sb0.35 SLS structures, the apparent out-of-plane strain states of the superlattices switch from tensile at deposition to compressive at operation. These changes have ramifications for material characterization, defect generation, carrier lifetime, and overall device performance of superlattices grown by MBE

Polarization Sensitivity of Quantum Well Infrared Photodetector Coupled to a Metallic Diffraction Grid

We study experimentally and numerically the polarization sensitivity of quantum well infrared photodetectors coupled to a diffraction grid. The polarization extinction ratio of such system is determined by two factors: polarization sensitivity of the diffraction grid and the intrinsic polarization sensitivity of the photodetector itself. The combined effect of these factors result in nonmonotonic dependence of the polarization extinction ratio on the parameters of the diffraction grid. By varying the grid parameters, i.e., increasing the height and tuning the grid period, a maximum value for the polarization extinction ratio can be achieved. Both front side and back side illuminations of the photodetector are studied. The strongest polarization sensitivity is achieved under front side illumination.Peer reviewed: YesNRC publication: Ye

Photodetector Focal Plane Arrays Integrated with Silicon Micropyramidal Structures in MWIR

Light-concentrating truncated Si micropyramidal arrays with 54.7 degree sidewall angles were successfully integrated with PtSi Schottky barrier photodetectors. Four different devices consisting of 10 x 10 photodetectors with 60 um pitch combined in parallel were tested, where significant enhancement capability was demonstrated by the Si micropyramids. The device consisting of one hundred 22 um square detectors monolithically integrated with the light-concentrating micropyramidal array displayed signal enhancement of up to 4 times compared to the same size 22 um square photodetector device without the light concentrators

Focusing and Diffraction of Light by Periodic Si Micropyramidal Arrays

This research was devoted to modeling of the optical properties of Si micropyramids aimed at designing optimal structures for applications as light concentrators in mid-wave infrared (MWIR) focal place arrays (FPAs). It is shown that completely different optical properties of such structures can be realized using two types of boundary conditions (BCs): i) periodical and ii) perfectly matched layer. The first type (periodical BC) allowed us to describe the Talbot effect under plane wave coherent illumination conditions. This effect was experimentally demonstrated in the proposed structures. The second type (perfectly matched layer BC) allows describing the optical properties of individual micropyramids concentrating or focusing light on the photodetector. The optimal geometries of micropyramids required for maximizing the intensity of photonic nanojets emerging from their truncated tips are determined

Al fraction induced effects on the capacitance characteristics of n+-GaN/Al x Ga 1-x N IR detectors

Capacitance-voltage-frequency measurements on n+-GaN/AlxGa1-xN Heterojunction Interfacial Workfunction Internal Photoemission (HEIWIP) detectors were used to analyze the effects of Al fraction induced heterojunction barrier and its effect on the electrical characteristics at the heterointerface. The detector's IR threshold can be modified by changing the barrier Al concentration. A sample with an Al fraction of 0.1 shows a distinct capacitance step and capacitance hysteresis, which is attributed to N-vacancies and/or C-donor electron trap states located just above the Fermi level (200 meV) at the GaN/AlGaN interface, with activation energies of 149\ub11 and ~189 meV, respectively. A sample with an Al fraction of 0.026 showed negative capacitance and dispersion, indicating interface electron trap states located below the Fermi level (88 meV), most likely due to C-donor and/or N-vacancy with activation energies of 125\ub11 and 140\ub12 meV, respectively. Additional impurity related absorption centers were identified in both samples, however these shallow Si-donor sites (~30.9\ub10.2 meV) did not affect the capacitance as these states were located in the barrier layer and not in the vicinity of the Fermi level. The Al fraction in the barrier layer was found to significantly change the positions of the interface trap states relative to the Fermi level, resulting in the observed capacitance characteristics.Peer reviewed: YesNRC publication: Ye