Extended Cutoff Wavelength Research Articles

Deriving the absorption coefficients of lattice mismatched InGaAs using genetic algorithm

Lattice-mismatched InGaAs has appeared to be emerging semiconductor materials for sensors and photovoltaic applications. The absorption coefficients of the materials are crucial in designing high-performance semiconductor devices. Nevertheless, the absorption coefficient of lattice-mismatched InGaAs were not comprehensively studied to cater for the 2000–3000 nm applications. This study aims to determine the absorption coefficients of lattice-mismatched In0.73Ga0.27As and In0.83Ga0.17As semiconductor materials through photocurrent measurement which enables the absorption tail information to be extracted. In addition, this work demonstrates the incorporation of an innovative artificial intelligence-based method in solving the absorption coefficient of lattice-mismatched InGaAs, considering the detailed information of the structure design and material parameters. By selecting the best gene for the next iteration, the utilization of Genetic Algorithm has significantly reduced the number of iterations from a maximum of 10 000 to 300. Validation of the algorithm was conducted, showing a good agreement of absorption coefficient result compared to the published work on In0.72Ga0.28As. The absorption coefficient of In0.83Ga0.17As with an extended cutoff wavelength near 2.6 μm is newly reported in this paper. In addition, the extrapolation of the obtained absorption results demonstrates energy gaps of 0.475 eV for In0.73Ga0.27As and 0.55 eV for In0.83Ga0.17As, which are compatible with the reported bandgaps of these materials. The extracted absorption coefficient information can be used in the design of semiconductor devices for emerging technologies such as focal plane array, short wave infrared sensing and thermophotovoltaic.

Extended-SWIR Photodetection in All-Group IV Core/Shell Nanowires

Group IV Ge1-xSnx semiconductors hold the premise of enabling broadband silicon-integrated infrared optoelectronics due to their tunable bandgap energy and directness. Herein, we exploit these attributes along with the enhanced lattice strain relaxation in Ge/Ge0.92Sn0.08 core-shell nanowire heterostructures to implement highly responsive, room-temperature short-wave infrared nanoscale photodetectors. Atomic-level studies confirm the uniform shell composition and its higher crystallinity with respect to thin films counterparts. The demonstrated Ge/Ge0.92Sn0.08 p-type field-effect nanowire transistors exhibit superior optoelectronic properties achieving simultaneously a relatively high mobility, a high ON/OFF ratio, and a high responsivity, in addition to a broadband absorption in the short-wave infrared range. Indeed, the reduced bandgap of the Ge0.92Sn0.08 shell yields an extended cutoff wavelength of 2.1 um, with a room-temperature responsivity reaching 2.7 A/W at 1550 nm. These results highlight the potential of Ge/Ge1-xSnx core/shell nanowires as silicon-compatible building blocks for nanoscale integrated infrared photonics.

High-Performance GeSn Photodetector Covering All Telecommunication Bands

We report the design and fabrication of a high-speed GeSn normal-incidence p-i-n photodetector. To realize high-speed detection in all telecommunication bands, we optimize the Sn content in the absorption layer, the absorption-layer thickness, and the device size. The responsivity of the 18-μm-diameter device at 1550 nm reaches 0.32 A/W with an extended cutoff wavelength of 1700 nm and a 3-dB bandwidth as high as 28 GHz under -3 V bias, clear open eye diagrams are also obtained under zero bias at 1630 nm. All the results indicate that the device has a significant potential for applications in Si-based optical telecommunication in all telecommunication bands.

Ferroelectric Enhanced Performance of a GeSn/Ge Dual-Nanowire Photodetector.

GeSn offers a reduced bandgap than Ge and has been utilized in Si-based infrared photodetectors with an extended cutoff wavelength. However, the traditional GeSn/Ge heterostructure usually consists of defects like misfit dislocations due to the lattice mismatch issue. The defects with the large feature size of a photodetector fabricated on bulk GeSn/Ge heterostructures induce a considerable dark current. Here, we demonstrate a flexible GeSn/Ge dual-nanowire (NW) structure, in which the strain relaxation is achieved by the elastic deformation without introducing defects, and the feature dimension is naturally at the nanoscale. A photodetector with a low dark current can be built on a GeSn/Ge dual-NW, which exhibits an extended detection wavelength beyond 2 μm and enhanced responsivity compared to the Ge NW. Moreover, the dark current can be further suppressed by the depletion effect from the ferroelectric polymer side gate. Our work suggests the flexible GeSn/Ge dual-NW may open an avenue for Si-compatible optoelectronic circuits operating in the short-wavelength infrared range.

Towards Surface Leakage Free High Fill-Factor Extended Wavelength InGaAs Focal-Plane Arrays

By incorporating of a combined mesa cleaning of SF 6 plasma bombarding and HCl rinsing prior to the SiN x passivation, an ultra-low dark current density of 9.1 nA/cm 2 at 180 K under a reverse bias of -10 mV for 30 μm pitch In 0.83 Ga 0.17 As focal plane arrays (FPAs) with an extended cutoff wavelength of 2.6 μm has been achieved. Six times higher dynamic differential resistance-area product of 35 Ω · cm at 300 K and increased activation energies for dark current were also attained in comparison to reference FPAs. Shockley-Read-Hall lifetimes of ~40 and ~200 ns at 300 and 180 K were determined from theoretical simulation analyses, respectively. These results suggest such methods effectively remove the low resistance leakage pathways on the micro-mesa sidewall surfaces, and are essential for large format and high fill-factor FPAs with negligible surface leakage current.

Mid-Infrared InAs/InAsSb Superlattice nBn Photodetector Monolithically Integrated onto Silicon

Mid-infrared (MIR) silicon photonics holds the potential for realizing next generation ultracompact spectroscopic systems for applications in gas sensing, defense, and medical diagnostics. The direct epitaxial growth of antimonide-based compound semiconductors on silicon provides a promising approach for extending the wavelength of silicon photonics to the longer infrared range. This paper reports on the fabrication of a high performance MIR photodetector directly grown onto silicon by molecular beam epitaxy. The device exhibited an extended cutoff wavelength at ∼5.5 μm and a dark current density of 1.4 × 10–2 A/cm2 under 100 mV reverse bias at 200 K. A responsivity of 0.88 A/W and a specific detectivity in the order of 1.5 × 1010 Jones was measured at 200 K under 100 mV reverse bias operation. These results were achieved through the development of an innovative structure which incorporates a type-II InAs/InAsSb superlattice-based barrier nBn photodetector grown on a GaSb-on-silicon buffer layer. The difficulties in growing GaSb directly on silicon were overcome using a novel growth procedure consisting of an efficient AlSb interfacial misfit array, a two-step growth temperature procedure and dislocation filters resulting in a low defect density, antiphase domain free GaSb epitaxial layer on silicon. This work demonstrates that complex superlattice-based MIR photodetectors can be directly integrated onto a Si platform, which provides a pathway toward the realization of new, high performance, large area focal plane arrays and mid-infrared integrated photonic circuits.

Significantly extended cutoff wavelength of very long-wave infrared detectors based on InAs/GaSb/InSb/GaSb superlattices

The authors report significant tunability of the bandgap in very long-wave infrared (VLWIR) InAs/GaSb/InSb/GaSb superlattices. Calculations using the empirical tight binding method have shown the flexibility in tuning the energy levels of the valence band by inserting a thin InSb layer in the middle of the GaSb layer of a normal type-II binary InAs/GaSb superlattice. Through the experimental realization of several barrier structure photodiodes with 15 ML InAs/7 ML GaSb active region, the cutoff wavelength was extended from 14.5 μm to 18.2 μm by inserting 0.6 ML InSb at different locations in GaSb layer. The agreement between the theoretical predictions and the experimental measurement suggests a way to exploit this advantage for the realization of very long-wave infrared detection without increasing the thickness of InAs layer. At 77 K, the quantum efficiency of a very long-wave detector with the cutoff wavelength of 16.9 μm reached at a maximum value of 30%, and the R0A is kept at a stable value of 10 Ω cm2 with the peak detectivity of 2.73 × 1011 cm Hz1/2/W. The operability and the uniformity in responsivity of the 320 × 256 very long-wave focal plane arrays were 88% and 80%. The noise equivalent temperature difference at 65 K presents a peak at 25 mK, corresponding to an average value of 60 mK, with an integration time of 0.5 ms, a 300 K background, and f/2 optics.

<inline-formula> <tex-math notation="TeX">\(640\times 512\) </tex-math></inline-formula> Extended Short Wavelength Infrared In<sub>0.83</sub>Ga<sub>0.17</sub>As Focal Plane Array

We present the detailed characteristics of solid source molecular beam epitaxy (MBE) grown large format ( \(640\times 512\) ) extended short wavelength infrared In0.83Ga0.17As sensor with desirable performance at both pixel and focal plane array (FPA) levels. The FPA pixels in the mesa structure grown on a graded AlInAs buffer layer with 2.65- \(\mu \) m, 300-K cutoff wavelength exhibited 300- and 200-K peak detectivities as high as \(\sim \!\! 2.5\times 10^{10 }\) and \(\sim \!\!1\times 10^{12}\) cmHz \(^{1/2}\) /W, which are both equivalent to the theoretical limits set by the Johnson noise of the detector. Dark current analysis of the pixels displayed no considerable tunneling component with the dark current being dominated by generation-recombination and shunt leakage mechanisms >200 K up to a reverse bias voltage of 3 V. Moreover, the noise measurements displayed no 1/ \(f\) noise in the FPA pixels. In spite of the large lattice mismatch, the FPA yielded very good response linearity, as well as impressively good responsivity nonuniformity and pixel operability of 5.5% and 99.8%, respectively. The results showing the feasibility of both solid source MBE and graded AlInAs buffer for the growth of extended InGaAs photodetectors are very encouraging for the large format FPA implementation of these detectors with desirable imaging performance and an extended cutoff wavelength as high as \(\sim 2.7\) \(\mu \) m.

Interband cascade infrared photodetectors with long and very-long cutoff wavelengths

We report our recent studies of interband cascade infrared photodetectors (ICIPs) with 100% cutoff wavelengths of 16.0μm and 9.2μm at 78K. The very-long-wavelength infrared (VLWIR) detectors were able to operate at temperatures up to 143K. Relatively high dark current densities were observed from these VLWIR detectors. This was attributed to the very narrow bandgap and possibly to defects in the materials. In addition, the photo-response of these detectors was strongly dependent on bias, indicating that further research and device optimization are necessary. Two-stage ICIPs in the long-wavelength infrared (LWIR) spectrum (8–12μm) were able to operate at higher temperatures (up to 250K) with an extended cutoff wavelength of ∼12μm. At 78K, these LWIR detectors had a bias-independent photocurrent, with an R0A of 115Ωcm2. This corresponded to a Johnson-noise-limited D∗ of 3.7×1010cmHz1/2/W at 8.0μm.

Development of quantum well, quantum dot, and type II superlattice infrared photodetectors

We present an overview of III-V semiconductor-based infrared detector and focal plane array development at the NASA Jet Propulsion Laboratory in recent years. Topics discussed include: (1) the development of long-wavelength quantum well infrared photodetector for imaging spectrometer applications, (2) the concept and realization of the submonolayer quantum dot infrared photodetector (SML-QDIP) as an alternative to the standard QDIP-based on Stranski-Krastanov (SK) quantum dots, (3) the mid-wavelength infrared quantum dot barrier infrared detector with extended cutoff wavelength, and (4) high-performance type-II superlattice long-wavelength infrared detectors based on the complementary barrier infrared detector architecture.

Mid-infrared quantum dot barrier photodetectors with extended cutoff wavelengths

A method to extend the cutoff wavelength of mid-infrared barrier photodetectors by incorporating self-assembled InSb quantum dots into the active area of the detector is demonstrated. This approach enables the extension of the cutoff wavelength of barrier photodetectors from 4.2 to 6 m, demonstrating infrared response at temperatures up to 225 K.

Interface structure and electrical properties of PtSi/Si1-xGexdiodes based on silicon

PtSi/strained Si1−xGe x (x=0, 0.2, and 0.25) Schottky-barrier diodes (SBD) with extended cutoff wavelengths have been demonstrated by combining pulsed laser deposition (PLD) and molecular beam epitaxy (MBE). Pt was deposited by PLD on the Si1−xGe x alloys with a thin Si sacrificial cap layer fabricated by MBE. By the reaction of deposited Pt film on Si, a sacrificial cap layer silicide SBD has been fabricated. Auger electron depth profiling was performed on the films before and after in vacuo annealing to study the redistribution of composition in the reactions. High-resolution transmission electron microscopy was used to investigate the interface structure. We have found that Pt reacts mainly with Si to form silicides at 350 °C, leaving some Ge to segregate at the surface. With annealing at 600 °C for 3 min the interface of PtSi/Si1−xGe x is smooth. Since lowered-barrier-height silicide SBD are desirable for obtaining longer cutoff wavelength Si-based infrared detectors, the Schottky barrier heights of the PtSi/strained Si1−xGe x SBDs with smooth interfaces were substantially lower than those of PtSi/Si SBDs, i.e., decreased with increasing Ge fraction, allowing for tuning of the SBDs cutoff wavelength. At 293 K, the ideality factor has been found to be 2.00 and 1.32 for PtSi/Si0.80Ge0.20 and PtSi/Si0.75Ge0.25 diodes, respectively. We have shown that high quantum efficiency and near-ideal dark current can be obtained in the film of PtSi/strained Si1−xGe x with an excellent interface fabricated by MBE and PLD, after annealing at 600 °C for 3 min.

Interfacial composition and electrical properties of PtSi/Si 1− xGe x/Si diodes by molecular beam epitaxy (MBE) and pulsed laser deposition (PLD)

By combining pulsed laser deposition (PLD) and molecular beam epitaxy (MBE), it has been demonstrated that PtSi/strained Si 1− x Ge x ( x=0,0.2 and 0.25) Schottky barrier detector (SBD) with extended cutoff wavelengths. Pt was deposited by PLD on the Si 1− x Ge x alloys with a thin Si sacrificial cap layer grown by MBE. By the reaction of deposited Pt film on Si sacrificial cap layer silicide SBDs have been fabricated. Auger electron depth profiling was performed on the films before and after in vacuo annealing to study the redistribution of composition in the reactions. The variation of the barrier height of the junctions with the Ge fraction x was studied, it was found to follow the same change as the bandgap of strained Si 1− x Ge x , and the cutoff wavelength has been extended beyond 10 μm in PtSi/strained Si 1− x Ge x SBDs. In addition, the Schottky barrier height (SBH) of PtSi/Si 1− x Ge x /Si has been found to vary between 0.12 and 0.58 eV in the temperature range 77–293 K. At 293 K, the ideality factor has been found to be 2.00 and 1.32 for PtSi/Si 0.80Ge 0.20 and PtSi/Si 0.75Ge 0.25 diodes, respectively.

Doping-spike PtSi Schottky infrared detectors with extended cutoff wavelengths

A technique incorporating a p/sup +/ doping spike at the silicide/Si interface to reduce the effective Schottky barrier of the silicide infrared detectors and thus extend the cutoff wavelength has been developed. In contrast to previous approaches which relied on the tunneling effect, this approach utilizes a thinner doping spike (<2 nm) to take advantage of the strong Schottky image force near the silicide/Si interface and thus avoid the tunneling effect. The critical thickness, i.e., the maximum spike thickness without the tunneling effect has been determined and the extended cutoff wavelengths have been observed for the doping-spike PtSi Schottky infrared detectors. Thermionic-emission-limited and thermally assisted tunneling dark current characteristics were observed for detectors with spikes thinner and thicker than the critical thickness, respectively.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

7-μm-cutoff PtSi infrared detector for high sensitivity MWIR applications

PtSi Schottky infrared detectors with extended cutoff wavelengths of 5.7, 6.6, and 7.3 μm have been demonstrated by incorporating a thin p+ layer at the PtSi-Si interface for high sensitivity medium wavelength infrared imaging applications. The response uniformity of the 7-μm cutoff detector was studied.

Tailorable Doping-Spike PtSi Infrared Detectors Fabricated by Si Molecular Beam Epitaxy

By incorporating a 1-nm-thick p+ doping spike at the PtSi/Si intertace, we have successfully demonstrated extended cutoff wavelengths of PtSi Schottky infrared detectors. The extended cutoff wavelengths resulted from the reduced effective potential barriers due to the combined effects of an increased electric field near the silicide/Si intertace and the Schottky image force. The p+ doping spikes were grown by molecular beam epitaxy at 450° C using elemental boron as the dopant source, with doping concentrations ranging from 5×1019 to 2×1020 cm-3. The cutoff wavelengths were shown to increase with increasing doping concentrations of the p+ spikes. Thermionic emission dark current characteristics were observed and photoresponse in the LWIR regime was demonstrated. Furthermore, the effective potential barriers determined by the Richardson plots were used to study the electrically activated boron dopant concentrations of the thin (1-nm-thick) spikes.

Long-wavelength PtSi infrared detectors fabricated by incorporating a p+ doping spike grown by molecular beam epitaxy

By incorporating a 1-nm-thick p+ doping spike at the PtSi/Si interface, we have successfully demonstrated extended cutoff wavelengths of PtSi Schottky infrared detectors in the long wavelength infrared (LWIR) regime for the first time. The extended cutoff wavelengths resulted from the combined effects of an increased electric field near the silicide/Si interface due to the p+ doping spike and the Schottky image force. The p+ doping spikes were grown by molecular beam epitaxy at 450 °C using elemental boron as the dopant source, with doping concentrations ranging from 5×1019 to 2×1020 cm−3. Transmission electron microscopy indicated good crystalline quality of the doping spikes. The cutoff wavelengths were shown to increase with increasing doping concentrations of the p+ spikes. Thermionic emission dark current characteristics were observed and photoresponses in the LWIR regime were demonstrated.

Modeling of parasitic barrier effects in silicide/Si1−xGex Schottky-barrier infrared detectors fabricated with a silicon sacrificial layer

By employing a thin silicon sacrificial cap layer for silicide formation, we have fabricated both Pd2Si/Si1−xGex and PtSi/Si1−xGex Schottky-barrier infrared detectors with extended cutoff wavelengths and near-ideal leakage characteristics. Substantial deviation in the spectral response from Fowler’s theory was observed in some silicide/Si1−xGex detectors fabricated using this technique. This deviation was attributed to a parasitic barrier at the interface due to the excess silicon sacrificial layer left unconsumed by the silicide formation process. A simple model which modifies Fowler’s theory to take into account the reduced injection efficiencies of the photoexcited holes through the Si barrier was proposed. Good agreement between this model and the experimental data has been achieved.

Silicide/strained Si/sub 1-x/Ge/sub x/ Schottky-barrier infrared detectors

By employing a thin silicon sacrificial cap layer for silicide formation, the authors successfully demonstrated Pd/sub 2/Si/strained Si/sub 1-x/Ge/sub x/ Schottky-barrier infrared detectors with extended cutoff wavelengths. The sacrificial silicon eliminates the segregation effects and Fermi level pinning which occur if the metal reacts directly with Si/sub 1-x/Ge/sub x/ alloy. The Schottky barrier height of the silicide/strained Si/sub 1-x/Ge/sub x/ detector decreases with increasing Ge fraction, allowing for tuning of the detector's cutoff wavelength. The cutoff wavelength was extended beyond 8 mu m in PtSi/Si/sub 0.85/Ge/sub 0.15/ detectors. It is shown that high quantum efficiency and near-ideal dark current can be obtained from these detectors. >

Ion-Implanted Germanium Far-Infrared Photodetectors

ABSTRACTGermanium Blocked Impurity-Band (BIB) detectors, which have potential applications for space-born far infrared astrophysics observations, have been fabricated by means of boron ion implantation on high-purity Ge substrates. These devices are sensitive beyond the cutoff wavelength of Ge photoconductors doped with shallow acceptors. The extended cutoff wavelength increases with applied bias and can reach up to 200μm at very low dark currents of less than 100 electrons/sec. In order to enhance the photo-response, high-energy (3MeV) implantation has been used to form a thicker infrared-active layer. The influence of both ion-implant energies and post-implant anneals on the performance of detectors will be presented. Generation of excess donors in the boron implanted region has been observed. Their origin and effect of device performance will be discussed.