Superlattice Photodiodes Research Articles

The Influence of Etching Method on the Occurrence of Defect Levels in III-V and II-VI Materials.

The influence of the etching method on the occurrence of defect levels in InAs/InAsSb type-II superlattice (T2SLs) and MCT photodiode is presented. For both analyzed detectors, the etching process was performed by two methods: wet chemical etching and dry etching using an ion beam (RIE-reactive ion etching). The deep-level transient spectroscopy (DLTS) method was used to determine the defect levels occurring in the analyzed structures. The obtained results indicate that the choice of etching method affects the occurrence of additional defect levels in the MCT material, but it has no significance for InAs/InAsSb T2SLs.

Reduction of surface leakage current of InAs/GaSb long-wavelength superlattice detectors using SiO2 and anodic sulfide composite passivation

We investigate two passivation methods for long-wavelength infrared type-II InAs/GaSb superlattice (T2SL) photodiodes with the PπBN structure containing an InAs/AlSb hole barrier layer. In order to eliminate the surface defects of T2SL better to further reduce the surface dark current, anodic vulcanization and SiO2 composite passivation method is adopted to optimize the original SiO2 passivation method. At 77 K, the I–V curve of the devices under the two passivation methods are obtained. Compared with passivation-only SiO2, the dark current density of the anode sulfide and SiO2 composite passivation detector is reduced by one order of magnitude, and the surface resistivity is effectively improved by an order of magnitude. Additionally, the composite passivation method not only improves the uniformity of the device, but also prevents the peeling of the S layer to improve the quality of passivation. This work offers a stable and high-quality passivation method, and it could be popularized passivation in the field of optics, electronics, optoelectronics, and switching devices.

Characterisation, modelling and design of cut-off wavelength of InGaAs/GaAsSb type-II superlattice photodiodes

InGaAs/GaAsSb type-II superlattice (T2SL) photodiodes grown on InP substrates are an alternative detector technology for applications operating in the short wavelength infrared band. Their cut-off wavelengths are heavily influenced by the thickness and material composition of InGaAs and GaAsSb used in the T2SL. We present a single band k.p. model performed using a finite difference approach in nextnano validated against two T2SL photodiode wafers and results from literature. These photodiode wafers cover both lattice matched and strained GaAs1−x Sb x compositions (x = 0.40, wafer A and 0.49, wafer B). The validation data covers temperature dependence of cut-off wavelengths (obtained from phase-sensitive photo response data) from 200 K to room temperature. The cut-off wavelengths were found to reduce at 1.32 nm K−1 for wafer A and 1.07 nm K−1 for wafer B. Good agreement was achieved between the validation data and nextnano simulations, after altering the GaAs1−x Sb x valance band offset (VBO) bowing parameter to −1.06 eV. Using this validated model, we show that the wavefunction overlap drops significantly if the GaAsSb barrier is thicker than the InGaAs well layer, hence defining the upper limit of the barrier layer. This validated model is then used to demonstrate that there is a linear dependence between the maximum achievable wavefunction overlap and cut-off wavelength of a lattice matched InGaAs/GaAsSb T2SL. We also found that the adoption of a 5 nm/3 nm InGaAs/GaAsSb T2SL structure offers an improved wavefunction overlap over the more common 5 nm/5 nm InGaAs/GaAsSb T2SL designs. The data reported in this paper is available from doi: 10.15131/shef.data.20310591.

Improved performances InAs/AlSb Type-II superlattice photodiodes for eSWIR with Ldiff of 2.4 µm and QE of 38% at 300 K

We studied InAs/AlSb superlattice photodiodes grown on a GaSb substrate, for the extended short wavelength infrared range. Reducing the majority carrier concentration from 2 × 1016 cm−3 to 2 × 1015 cm−3 caused the carrier diffusion length, Ldiff, to increase from 1.4 µm to 2.4 µm, respectively. This, in turn, increased the front-side illuminated quantum efficiency, without anti reflecting coating, at 300 K, λ = 2.18 µm and −0.1 V from 19% to 38%. At 200 K the 50% cutoff wavelength was 2.45 µm, the dark current density at −0.1 V was 2.4 × 10−5 A/cm2 and the detectivity was 2 × 1011 cm-Hz1/2/W. Using a gating technique on the mesa sidewall surface enabled the reduction of the dark current density.

Graphene Based Heterojunction PIN Device as Photo-Sensor

In this paper, we propose to prospects of Multiple-Graphene-Layer (MGL) based vertically doped p ++-n-n - -n ++ Avalanche photo diode-sensor in visible wavelength region (400nm-700nm). At room temperature, the authors have studied the high carrier mobility, intrinsic optical and mechanical properties in Graphene in various novel applications. To study the comparative analysis between the experimental and analytical observation of APD sensor, the authors have design, developed and experimentally verified Quantum-Corrected Field Maximum Classical Drift-Diffusion (QCFMCDD) mathematical model. The authors have compared the results with those of Si/4H- SiC super-lattice avalanche photo-diode sensor at 600 nm wavelength of incident radiation. It is noticed that Graphene performs better than Si/4H-SiC counterpart in terms of photo-responsivity (0.76A/W vs. 0.60A/W) and quantum efficiency (82% vs. 60%) for optical irradiation in visible wavelength region. The optical-electrical performance of 3x3 array type Graphene photo sensor diode is further analyzed and compared with those of its single array counterpart. In published literature, the available photo detector comprises with the designed photo-sensor shows the significant overall better performance in visible wavelength region.

Optimization of Long-Wavelength InAs/GaSb Superlattice Photodiodes With Al-Free Barriers

We demonstrate long-wavelength InAs/GaSb superlattice photodiodes grown on InAs substrates in a production-scale metal-organic chemical vapor deposition system. An aluminum-free heterojunction scheme was adopted where mid-wavelength superlattices served as electron barriers alongside an ${n}$ -type long-wavelength absorber. Both electrical modeling and experimental characteristics suggest that suppressed dark current and unimpeded transport of photo-generated carriers can be both achieved with engineered barrier layers. Under 77 K and a reverse bias of −0.1 V, the optimized device has shown a cut-off wavelength around 12 $\mu \text{m}$ , a blackbody responsivity of 1.01 A/W, a dark-current density of 5 $\times \,\,10^{-4}$ A/cm2 and a dark-current limited specific detectivity over 1 $\times \,\,10^{11}$ cm $\cdot \sqrt {\textrm {Hz}}$ /W.

Growth and characterization of type-II superlattice photodiodes with cutoff wavelength of 12 μm on 4-in. wafer

High performance InAs/GaSb superlattices for long-wavelength infrared detection were grown on a 4-in. GaSb wafer using molecular beam epitaxy. The influence of the growth temperature, V/III BEP ratio on the surface morphology and microstructure was researched. The good uniformity of the surface roughness and crystallization at four location along the radial direction on the wafer was obtained by balancing the inner and outer growth temperature. The performance deviation of the four photodiodes fabricated using the superlattices from center to edge on the wafer was below 20% which revealed the uniformity of the superlattice growth and the fabrication process. The 50% cutoff wavelength was about 12 μm. The peak responsivity was 2.54 A/W corresponding to a quantum efficiency of 35.1% at 77 K. The zero bias differential resistance-area product (R0A) was 2.1 Ω cm2 due to the barrier structure design which restrains the diffusion dark current. The calculated Johnson noise limited detectivity was 5.75 × 1010 cm √Hz/W at 10 μm and 4.13 × 1010 cm √Hz/W at 14 μm.

Inductively coupled CH 4 /H 2 plasma etching process for mesa delineation of InAs/GaSb type‐II superlattice pixels

An inductively coupled plasma etching process for delineation of InAs/GaSb type-II superlattice pixels is presented. An optimised etch recipe without alternate plasma cleaning step showed an etch rate as high as 0.11 μm/min that results in smooth vertical sidewalls for the type-II superlattice pixel arrays with 10 μm pitch size and 2.4 μm deep trenches. At 70 K, the dark current density for the mesa etched + SU-8 polymer passivated type-II superlattice photodiodes was found to be 0.11 A/cm2 at an applied reverse bias voltage of 0.2 V. The activation energy of 13 meV obtained from the Arrhenius plot and a variable area diode array technique showed that the measured dark current is mainly attributed to bulk tunnelling current. This technique of mesa delineation for the type-II superlattice pixel arrays with small pitch size is a viable option in realising next-generation infrared focal plane arrays.

High quantum efficiency mid-wavelength infrared type-II InAs/InAs1−xSbx superlattice photodiodes grown by metal-organic chemical vapor deposition

We report the growth and characterization of mid-wavelength infrared type-II InAs/InAs1−xSbx superlattice photodiodes on GaSb substrates grown by metal-organic chemical vapor deposition. At 150 K, the 50% cut-off wavelength is 5.0 μm, the dark current density is 3.3 × 10−4 A/cm2 under −20 mV bias, and the peak responsivity is 1.76 A/W corresponding to a quantum efficiency of 55% without anti-reflection coating. A specific detectivity of 1.2 × 1011 cm Hz1/2/W is achieved at 4.0 μm under −20 mV bias at 150 K.

Influence of shallow versus deep etching on dark current and quantum efficiency in InAs/GaSb superlattice photodetectors and focal plane arrays for long wavelength infrared detection

In this paper, a comparison of quantum efficiency and dark current densities of shallow etched and deep etched InAs/GaSb type-II superlattice photodiodes is presented. The detectors were tailored for space applications with measured cut-off wavelengths around 11.2 µm. Bias and temperature dependencies of the QE have been studied showing very low turn on bias (>−25 mV) and very small variation of the peak QE value with temperature. At 70 K, peak quantum efficiencies of shallow and deep etched devices were deduced to 34% and 30%, respectively (without antireflection coating). The difference was attributed to a larger collection area of shallow etched devices, with a collection range of approximately 22 µm outside of the defined pixel area. Diffusion limited dark currents were observed down to 60 K for both shallow and deep etched devices under low reverse bias (∼−200 mV) with dark current densities on the order of 1.7 × 10−5 A/cm2 at 60 K. A gradually increasing influence of generation-recombination (G-R) and trap-assisted tunneling (TAT) was observed at lower temperatures for high reverse bias. The lowest dark current densities were observed for deep etched photodiodes, on the order of 3 × 10−7 A/cm2 at 40 K (Vbias = −100 mV). Detector arrays were fabricated with deep etched 30 µm pitch pixels. Comparably low dark current densities were observed for the detector array pixels under low reverse bias as for the single pixel photodiodes, however a significant increase of the TAT dark current was observed under high reverse bias.

Demonstration of long wavelength infrared type-II InAs/InAs1-xSbx superlattices photodiodes on GaSb substrate grown by metalorganic chemical vapor deposition

We report the growth and characterization of long wavelength infrared type-II InAs/InAs1-xSbx superlattice photodiodes with a 50% cut-off wavelength at 8.0 μm on a GaSb substrate grown by metalorganic chemical vapor deposition. At 77 K, the photodiodes exhibited a differential resistance at zero bias (R0A) of 8.0 Ω cm2 and a peak responsivity of 1.26 A/W corresponding to a quantum efficiency of 21%. A specific detectivity of 5.4 × 1010 cm Hz1/2/W was achieved at 7.5 μm.

Investigation of deep level defects on Beryllium compensation doping of In0.53Ga0.47As/GaAs0.49Sb0.51 type-II superlattice photodiodes.

In this paper, deep level transient spectroscopy (DLTS) characterization was performed on Beryllium compensation doping of InGaAs/GaAsSb type-II superlattice photodiode. Three electron traps with the energy levels located at Ec-0.11 eV (E1), Ec-0.28 eV (E2), Ec-0.17 eV (E3), and a hole trap situated at Ev + 0.25 eV (H1) were revealed. The position distribution and depth concentration of these traps in SL absorption region was also explored. Furthermore, the bandlike states (E2) and localized states (E1 and H1) of extended defects were confirmed by DLTS measurements as a function of the filling-pulse time, these traps as generation-recombination centers are responsible for dominant dark current.

Direct growth of InAs/GaSb type II superlattice photodiodes on silicon substrates

p-i-n InAs/GaSb type II superlattice photodiodes were directly grown on silicon substrates. The superlattice structures were grown monolithically on miscut Si substrates via a 10 nm AlSb nucleation layer. Interfacial misfit array technique was used to accommodate the large lattice mismatch between III-Sb epi-layers and Si. Atomic force microscopy and X-ray diffraction measurements revealed degraded material quality of type II superlattices grown on Si, compared with the sample grown on GaAs. Photoluminescence characterization indicates comparable optical properties with about 39% deduction of peak intensity. Dark current measurements were also used to study the electrical properties of the samples.

Low dark current in mid-infrared type-II superlattice heterojunction photodiodes

A mid-infrared (MWIR, 3–5μm) InAs/GaSb type-II superlattice (T2SL) photodiode device with very low dark current is presented. The novel heterojunction device is compared to a conventional pn-homojunction device. Photodetectors with reduced dark current allow an increased operating temperature and thus to lower the cooling requirements for high performance infrared imaging applications. We report on a dark current reduction by a factor of more than 100 at a typical operation voltage of −100mV at 77K, which was realized merely by device design. This measured dark current is the lowest reported to our knowledge for T2SL-detectors operating in the 3–5μm range. At the same time, the photo current signal is unaffected by the heterostructure design over the entire bias voltage range.

Capacitance-voltage investigation of low residual carrier density in InAs/GaSb superlattice infrared detectors

Capacitance-voltage (CV) analysis was performed on homojunction InAs/GaSb superlattice photodiodes for the mid-infrared spectral range around 5μm. The CV investigation was carried out over a wide temperature range from 80K up to 200K, for two nominally identical samples from two different epitaxy systems. The characterizations were carried out with a refined measurement setup, considering the impedance range, the measured frequency range and the accessible temperature range. For the calculated residual carrier density in the nid-region of the diodes values in the low 1014cm−3 and 1015cm−3 ranges were found, respectively.

Performance comparison between the InAs-based and GaSb-based type-II superlattice photodiodes for long wavelength infrared detection.

In this paper, we report on the characterization of InAs/GaAsSb type-II superlattice long wavelength infrared photodiodes grown on InAs substrates by molecular-beam epitaxy and also present the device performance comparison with the superlattice devices grown on GaSb substrates. These devices with PIN structures had a 100% cutoff wavelength of 10 μm. The dark current density of InAs-based device at -30 mV reverse bias was 4.01 × 10-4 A/cm2 and the resistance-area product at zero bias (R0A) was 36.9 Ωcm2. The dark current density of GaSb-based device is higher more than one order of magnitude than that of InAs-based device. The temperature-dependence and bias-dependence of the dark current are studied experimentally and correlated to the theory. Good agreement was achieved between the measured I-V curves and the simulated ones, and between the experimental and theoretically predicted differential resistance values. Compared with InAs-based superlattice device, the generation-recombination current of GaSb-based device is larger and dominates in a wider temperature range due to shorter carrier lifetime and higher defect density.

Type-II InAs/GaSb photodiode array pixel isolation by femto-second laser anneal

A 775nm, 150fs laser anneal technique for increased inter-pixel isolation in type-II InAs/GaSb superlattice photodiode arrays (5.5μm cutoff wavelength) without mesa etch, is presented. With only p+ inter-pixel etch and fs laser anneal, a greater than two fold improvement in the inter-pixel isolation is observed at 70K. A similar reduction in the dark current of p+ etched+fs laser annealed p-i-n photodiodes is observed at 70K over un-passivated mesa etched photodiodes of 400μm pixel sizes, whereas in 55μm pixels a seven fold reduction in the surface component of dark current over un-passivated mesa etched diodes is achieved. An increased band gap of the inter-pixel region (∼10meV) due to fs annealed intermixing has been calculated to be a possible reason for the improved inter-pixel isolation.

Investigation of a near mid-gap trap energy level in mid-wavelength infrared InAs/GaSb type-II superlattices

In this report, we present results of an experimental investigation of a near mid-gap trap energy level in InAs10 ML/GaSb10 ML type-II superlattices. Using thermal analysis of dark current, Fourier transform photoluminescence and low-frequency noise spectroscopy, we have examined several wafers and diodes with similar period design and the same macroscopic construction. All characterization techniques gave nearly the same value of about 140 meV independent of substrate type. Additionally, photoluminescence spectra show that the transition related to the trap centre is temperature independent. The presented methodology for thermal analysis of dark current characteristics should be useful to easily estimate the position of deep energy levels in superlattice photodiodes.

Wet Chemical Etching of Antimonide-Based Infrared Materials**Supported by the National Basic Research Program of China under Grant Nos 2014CB643903, 2013CB932904, 2012CB932701 and 2011CB922201, the National Special Funds for the Development of Major Research Equipment and Instruments under Grant No 2012YQ140005, the National Natural Science Foundation of China under Grant Nos 61274013, U1037602 and 61290303, and the Strategic Priority Research Program

The roughness and the crystallographic orientation selectivity of etched antimonide-based infrared materials are examined and are used to optimize the chemical mesa etching process of the InAs/GaSb superlattice photodiode with the goal of reducing the dark current. The etchant used is based on phosphoric acid (H3PO4), citric acid (C6H8O7) and hydrogen peroxide (H2O2). The roughness of the mesa sidewalls and etching rates are compared and used to find an optimized etchant, with which we obtain optimized mid-wavelength infrared photodiodes possessing an R0A value of 466 ω·cm2 and a detectivity of 1.43 × 1011 cm·Hz1/2 W−1. Crystallographic orientation selectivity is seen in InAs etching, and also is seen in the InAs/GaSb superlattice wet chemical etching process.

Dark current improvement of the type-II InAs / GaSb superlattice photodetectors by using a gate bias control

The dark current of a type-II InAs/GaSb strained layer superlattice photodiode with an n-i-p structure is reduced by using an active gate bias technique. To make the gate structure on the mesa sidewall of the photodiode, we used Si3N4 and Ti/Au as a dielectric film and a gate metal, respectively. At 77 K, the dark current density of the photodiode with a gate bias (VG = −30 V) applied on the mesa side wall is reduced by more than one order of magnitude compared to the dark current density at zero gate bias. At 77 K, the product of the dynamic differential resistance and the area at a gate bias of −30 V shows a 12 times improvement compared to the same measurement at zero gate bias.