Generation-recombination Current Research Articles

Comparison of type II superlattice InAs/InAsSb barrier detectors operating in the mid-wave infrared range

Four types of barrier detectors based on a type II InAs/InAsSb superlattice with a wide-gap barrier made of a solid AlInAsSb lattice matched to the GaSb buffer were compared. The tested detectors differed in the type of doping of the active layer and the level and type of doping of the contact layer at the barrier. The epitaxial layers were deposited on GaAs (100) substrates using the molecular beam epitaxy method. The spectral and current–voltage characteristics of the analyzed detectors were compared. The highest current responsivities were observed in the structure with a p-type absorber (p+BpN+). Detectors with an n-type absorber (p+Bnn+, n+Bnn+, and nBnn+) show an increase in the current responsivity with an increase in the reverse bias voltage due to the reduction in the undesirable barrier in the valence band. Arrhenius characteristics for the dark current show that only in nBnn+ detectors, it was possible to limit the generation–recombination current. These detectors at 150 K were characterized by the highest normalized detectivity of approximately 3 × 1011 cm · Hz1/2/W. The obtained results were compared with literature data, showing that the parameters of type II superlattice photodetectors are close to those of HgCdTe photodiodes according to the “Rule 07” and “Rule 22” principles.

Effect of “M” and “B” superlattice barrier layers on dark current of long-wavelength infrared detectors

This paper studies superlattice materials with M barrier (InAs/GaSb/AlSb/GaSb superlattice) and B barrier (InAs/AlSb superlattice) structures. Firstly, it introduces the diffusion current, generation-recombination current, tunneling current and surface leakage current in devices, and analyzes the factors affecting different dark current mechanisms. Secondly, it theoretically analyzes the influence of the two barrier structures on device performance. Finally, devices were fabricated using these two structures, and the device performance was characterized. At a bias voltage of −50 mV and operating temperature of 77K. The PπMN type long-wave infrared (LWIR) detector has an RA of 91.4 Ω cm2 and a LW dark current density of 3.51 × 10−4 A cm−2. The PπBN type LWIR detector has an RA of 439 Ω cm2 and a LW dark current density of 2.81 × 10−4 A cm−2. Meanwhile, by fitting the data at different temperatures, the activation energy Ea of the PπMN type LWIR detector is 119.8 meV, with dark current mainly determined by diffusion current and generation-recombination current. The activation energy Ea of the PπBN type LWIR detector is 126.2 meV, with dark current mainly determined by diffusion current. This experimentally verifies the dominant dark current mechanisms for the two barrier structures of LWIR detectors, providing strong support for the design of superlattice detector structures.

Long-wave bilayer graphene/HgCdTe based GBp type-II superlattice unipolar barrier infrared detector

Type-II superlattice (T2SL) material is used to design highly efficient next-generation infrared (IR) detectors. The flexibility of the material allows the integration of unipolar barrier IR detector architecture to suppress generation-recombination currents by blocking the majority charge carriers and improve device performance. This paper presents a self-powered T2SL unipolar barrier detector that operates in the long-wave IR regime. It comprises a contact layer made of p+-bilayer graphene (G) and a barrier layer made of p–-Hg1–xCdx=0.41Te (B) placed over a p+-Hg1–xCdx=0.2217Te absorber layer (p) and is known as the GBp detector. The optoelectronic characterization of the unipolar GBp detector is carried out using the Silvaco Atlas TCAD software. Under self-powered mode operation, the proposed GBp detector exhibits an improvement in photocurrent density of about 108 times. The dark current density of 0.4nA/cm2, the photocurrent responsivity of 7.82 A/W, the quantum efficiency of 91.44%, and the detectivity of 4.48 × 1014 cmHZ1/2/W are found at the liquid nitrogen temperature with a bias of –0.5 V. A dichroic ratio of 249 and a response time of less than 1 ps are likewise exhibited by the GBp detector. The substantial electric field at the contact/barrier heterointerface and the high barrier height in the conduction band, which result in an increased photodetection response, are attributed to this improved performance.

Dark current modeling of thick perovskite X-ray detectors

Metal halide perovskites (MHPs) have demonstrated excellent performances in detection of X-rays and gamma-rays. Most studies focus on improving the sensitivity of single-pixel MHP detectors. However, little work pays attention to the dark current, which is crucial for the back-end circuit integration. Herein, the requirement of dark current is quantitatively evaluated as low as 10−9 A/cm2 for X-ray imagers integrated on pixel circuits. Moreover, through the semiconductor device analysis and simulation, we reveal that the main current compositions of thick perovskite X-ray detectors are the thermionic-emission current (JT) and the generation-recombination current (Jg-r). The typical observed failures of p–n junctions in thick detectors are caused by the high generation-recombination current due to the band mismatch and interface defects. This work provides a deep insight into the design of high sensitivity and low dark current perovskite X-ray detectors.Graphical

Facet effects on generation-recombination currents in semiconductor laser diodes

The contribution of facet defect currents to the overall generation-recombination current of laser diodes operating near 800 nm is quantified experimentally, using the dependence of current on cavity length to isolate facet effects. The results show that facet currents exhibit an ideality factor much greater than 2, while currents associated with the interior of the laser diode stripes exhibit an ideality factor of 2. These differences in behavior provide an approach to infer additional details of defect evolution in aging studies of semiconductor laser diodes.

Analysis of dislocations and their correlation with dark currents in CdTe/Si heterojunction diode-type x-ray detectors

Distribution and density of dislocations as a function of CdTe epilayer thickness as well as their effect on device dark current were studied using a p-CdTe/n-CdTe/n+-Si heterojunction diode type x-ray detector. A high dislocation density was found in thin devices, which decreased by more than an order of magnitude when the device thickness was increased to 35 μm. First, the dislocation density decreased rapidly with the CdTe thickness but the decrement was slowed down for the CdTe thicknesses above 20 μm. The device dark current showed a strong dependence on dislocation density, which increased with an increase in the dislocation density. A nearly temperature independent dark current was observed in thin devices suggesting that trap-assisted tunneling (TAT) through the dislocation-related current paths was dominant. Dark currents of thicker devices, on the other hand, could be explained due to contributions from both TAT and generation-recombination currents. Furthermore, one possible detector design that helps us to reduce the dark current is also proposed.

Progress of long wavelength infrared focal plane arrays based on antimonide compounds superlattice

<p indent=0mm>The research of antimonide compounds began with 1950s. With the appearing of superlattice concept and energy band engineering in the 1970s, the potentials in infrared detection of antimonide compounds gradually emerged. Due to the reality demand, epitaxy and preparation technologies of antimonide-based materials have achieved rapid progress. The rapid advance of T2SL also benefits from the previously five decades ago of development of III-V group materials and devices research. The development of InAs/GaSb type-II superlattices (T2SLs) results from two primary motivations: the InAs/GaSb superlattice has more apparent advantages than HgCdTe in low cost, reproducibility, operability and high uniformity, especially for long wavelength detector. Secondly, the Auger recombination probability of type II superlattices is lower than that of HgCdTe, which means that the infrared detector of type II superlattice has a lower dark current or a higher working temperature than that of HgCdTe detector. And improving the working temperature of the long-wave focal plane is crucial for reducing the power consumption, size and weight of the imaging system. In addition, the atmosphere window with highest transmittance is located at the range of <sc>8−14 μm.</sc> And the emitted infrared radiation by an object at room temperature <sc>(300 K)</sc> has a wavelength of about <sc>10 μm.</sc> Therefore, long wavelength infrared detection is extremely valuable for InAs/GaSb type-II superlattices. Compared with HgCdTe device, T2SL detectors can provide equivalent or better performance under the same cutoff wavelength. But the short minority carrier lifetime of InAs/GaSb superlattice cause a high level of generation-recombination current (<italic>J</italic>_gr). In order to suppress <italic>J</italic>_gr and other dark current, the different device structures like W-structure, PπMN structure, CBIRD and unipolar barrier were put forward and employed in the detectors. As a result, the dark current and impedance was greatly improved. Furthermore, with the putting forward of InAs/InAsSb superlattice, the defects level in band gap introduced by Ga were avoided, and the minority carriers lifetime were effectively improved. The reproducibility, operability and uniformity of T2SL bring more advantages than HgCdTe detector with the sustainable developement of T2SL technologies and theories.

Ar Ion Irradiation Effects on the Characteristics of Ru|Pt|n-GaN Schottky Barrier Diodes

The present study reports the effects of 650-keV Ar2+ ion irradiation on the structural, optical, and device characteristics of Ru|Pt|n-GaN Schottky barrier diodes (SBDs). Ion irradiation induces the broadening of the GaN X-ray diffraction peaks due to induced structural deformities. The photoluminescence spectroscopy intensity decreases with the increase in the fluence of ions. The recombination of charge carriers induced by the geometrical distortions, and the formation of defects states, shifts the peak positions to shorter wavelengths. The electrical characteristics of these devices exhibit significant changes due to modification at the interface and charge transport properties after Ar2+ ion irradiation. The charge-transport properties are affected by these deformities at higher fluences and attributed to the contributions of various current conduction mechanisms, including defect-assisted tunnelling and generation-recombination (G-R) currents along with thermionic emission.

Effects of different passivation layers on RV characteristics of long-wave HgCdTe gate-controlled diodes

This work investigated the effect of different surface passivation layers on the electrical properties of long-wave HgCdTe photodiodes. For better comparison, three types of surface passivation methods, ZnS passivation, CdTe passivation, and ZnS/CdTe double passivation, were manufactured in one chip to produce gated diodes. The passivation film is the only difference between these devices. The experimental results show that under the gate voltage control, the diodes formed by the three passivation methods will experience the accumulation, flat band, depletion and inversion states below the gate structure. At the same time, the R-V characteristic curves of their dark currents can be well fitted to the existing model to obtain the diffusion current, the generation-recombination current, the trap assisted tunneling current, and the band-to-band tunneling current. However, different passivation layers have different gate voltage ranges corresponding to the same process. By fitting the body parameters obtained from the RV curve under the flat band voltage, it can be known that different surface passivation does not affect the device body parameters, and the surface bias formed by ZnS/CdTe double passivation has the most significant effect on the device. The ZnS and ZnS/CdTe double passivation films have similar insulating properties and are superior to CdTe passivation films.

Low-frequency noise limitations of InAsSb-, and HgCdTe-based infrared detectors

The 1/f noise in midwavelength InAsSb- and HgCdTe-based unipolar barrier infrared detectors, grown on GaAs substrate, are studied both experimentally and theoretically. The examination of the dark current reveals three current components: leakage, diffusion, and generation-recombination. The first dominates in the low-temperature region for all devices, while diffusion and generation-recombination components dominate in the high-temperature region. For InAsSb-based detectors with cut-off wavelength 5.6 μm at 230 K, the measured 1/f noise can be exclusively attributed to the leakage current (which has the surface origin), which means that noise coefficients (relative noise) of generation-recombination and diffusion currents are small with respect to the leakage-current induced 1/f noise. In the HgCdTe-based barrier detector with cut-off wavelength 3.6 μm at 230 K, all current components induce measurable 1/f noise, but the leakage current is effectively suppressed, consequently, 1/f noise connected with generation-recombination and diffusion currents can be isolated. For this detector, the relative 1/f noise of generation-recombination and diffusion current decrease versus temperature with an exponential manner but the relations between 1/f noise coefficients, observed for InAsSb-based devices, hold true. Then, an important conclusion is that the improvement in the above sensors detectivity, for slow varying signals, can be achieved by reducing the leakage current which can be the source of 1/f noise even at room temperature, where the total current is dominated by the diffusion component.

High performance nBn detectors based on InGaAsSb bulk materials for short wavelength infrared detection

We report a low dark current, high quantum efficiency nBn photodetectors based on In0.28Ga0.72As0.25Sb0.75 bulk materials with a cut-off wavelength of 3μm at room temperature. Generation-Recombination current was suppressed using an nBn design to shift deplete region from In0.28Ga0.72As0.25Sb0.75 active region into a wide band gap AlGaSb barrier region. The Arrhenius plots of R0A-1/T show that there is no Generation-Recombination current detected in nBn device, whereas pin devices have a Generation-Recombination dominant dark current at temperatures ranging from 160K to 220K. Optical characterizations at 300K show the nBn device using InGaAsSb as an absorption material has a relative high quantum efficiency. The nBn device exhibits a peak specific detectivity of 4.8×1010 Jones under 200mV reverse bias voltage at 300K. The low dark current, high quantum efficiency and band gap tunability are expected to make InGaAsSb bulk material a competitive candidate for short wavelength infrared regime.

Optical and Electrical Study of InAs/GaSb Type II Strained Layer Superlattice for Mid-wave Infrared Detector

This paper reports the results of modeling of optical and electrical characteristics of InAs/GaSb type II strained layer superlattice (SLS) for the mid-wave infrared detection with n-on-p polarity. The band gap calculation of the SLS was conducted as a function of the InAs and GaSb thickness, using a modified Kronig-Penny model. The cut off wavelength of the fabricated diode was ~ 6 μm (~ 0.2 eV) at 120 K. The product of zero-bias resistance and area (R0A) as a function of an applied bias was investigated in detail to analyze the dark current mechanisms. The thermal diffusion and generation-recombination current were dominant factors under low positive bias. However, as the reverse bias voltage increased, the trap assisted component became one of the dominant dark current factors.

InAs/InAsSb Type-II Superlattice Mid-Wavelength Infrared Focal Plane Array With Significantly Higher Operating Temperature Than InSb

We report focal plane array (FPA) results on a mid-wavelength InAs/InAsSb type-II strained layer superlattice (T2SLS) unipolar barrier infrared detector with a cutoff wavelength of 5.4 μm. For 300 K background in the 3–5-μm band, f/2 aperture, an FPA operating at 150 K exhibits a mean noise equivalent differential temperature (NEDT) of 18.5 mK, and an NEDT operability of 99.7%. The NEΔT distribution has a width of 8 mK, with no noticeable distribution tail, indicating excellent uniformity. The mean noise-equivalent irradiance is 9.1 × 1011 photons/sec-cm2. The mean quantum efficiency is 49.1% without antireflection coating, and the mean specific detectivity (D*) is 2.53 × 1011 cm-Hz½/W. Benefitting from an absorber material with a much longer Shockley–Read–Hall minority carrier lifetime, and a device architecture that suppresses generation-recombination and surface-leakage dark current, the InAs/InAsSb T2SLS barrier infrared detector FPA has demonstrated a significantly higher operating temperature than the mid-wavelength infrared market-leading InSb.

Performance Simulation of Unipolar InAs/InAs1−xSbx Type-II Superlattice Photodetector

This paper reports performance simulation of a unipolar tunable band gap InAs-InAsSb type-II superlattice (T2SL) infrared photodetector. The generation-recombination and surface leakage currents limit the performance of T2SL photodiodes. Unipolar nBn device design incorporating a suitable barrier layer in the diode structure is taken to suppress the Auger recombination and tunneling currents. At low reverse bias, the generation-recombination current is negligible in the absence of a depletion region, but the dark current is dominated by the diffusion current at higher operation temperatures. The composition, band alignment, barrier width, doping level and thickness of the absorber region are optimized here to achieve low dark current and high quantum efficiency at elevated operating temperatures. Thin unipolar T2SL absorbers are placed in a resonant cavity to enhance photon-material interaction, thus allowing complete absorption in a thinner detector element. It leads to the reduction in the detector volume for lower dark current without affecting the quantum efficiency. It shows an improvement in the quantum efficiency and reduction in the dark current. Dark current density ∼ 10−5 A/cm2 is achievable with low absorber thickness of 2 μm and effective lifetime of 250 ns in the InAs/InAs0.6Sb0.4/B-AlAs1−xSbx long wave length T2SL detector at 110 K.

Doping dependence of the contact resistivity of end-bonded metal contacts to thin heavily doped semiconductor nanowires

We study the resistivity, ρcN, of end-bonded contacts to semiconductor NanoWires (NWs) of radius R = 5–10 nm over doping Nd = 1018–1020 cm−3. The study is important for NW device design and characterization. It reports realistic calculations of ρcN and highlights and explains how ρcN differs significantly from the resistivity ρcB of bulk contacts. First, the space-charge width in NW contacts is increased by the surrounding field which depends on R, contact geometry, and ambient dielectric; this width also depends on surface charge and dielectric confinement which reduces dopant ionization. Second, thin NWs have a low effective lifetime, τN, due to surface recombination. Third, NW contacts have a lesser image force barrier lowering due to the higher space-charge width. Due to these factors, apart from tunneling (which decides ρcB), space-charge region generation-recombination current also affects ρcN. As Nd is raised from 1018 to 1020 cm−3, ρcB falls rapidly, but ρcN varies slowly and may even increase up to 3–5 × 1018 and then falls rapidly. Further, ρcN/ρcB can be ≪1 at Nd = 1 × 1018 cm−3, reaches a peak ≫1 around Nd = 1 × 1019 cm−3, and → 1 at Nd = 1 × 1020 cm−3, e.g., for 0.8 V contact barrier on 10 nm thick n-type silicon NWs with τN = 1 ps embedded in SiO2, at T = 300 K, even a 10 nm contact extension yields a peak of 75 at Nd = 8 × 1018 cm−3. We study changes in ρcN/ρcB versus Nd behavior with R, contact geometry, ambient dielectric, surface charge, τN, T, tunneling mass, and barrier height.

Dark current transport mechanism associated with acceptor concentration in GaAs-based blocked-impurity-band (BIB) detectors

Dark current transport mechanism associated with acceptor concentration in GaAs-based blocked-impurity-band (BIB) detectors has been investigated. Device structure, numerical models and simulation techniques are described in detail. By careful model and parameter calibration, the numerical simulation is completely consistent with the analytical calculation, proving the validity of simulation methods. Our results reveals that the carrier-transport modes of GaAs-based BIB detectors can be classified into two categories (i.e., electron current and hopping current), and the hopping current can be neglected compared with the electron current. Besides, it is demonstrated that the dark current of GaAs-based BIB detector is dominated by the drift–diffusion current and the generation-recombination current, and the both current components are monotonically decreasing functions of the acceptor concentration.

Generation recombination suppression via depletion engineered heterojunction for alternative substrate MWIR HgCdTe infrared photodetectors

We show suppression of generation-recombination dark current that leads to an increase in the operating temperature nearly 40 K (from ∼85 K to ∼125 K, τSRH = 200 ns) with diffusion limited performance of alternative substrate multiwafer infrared HgCdTe infrared photodetectors with a cut-off wavelength of 5 μm. Enhancement has been achieved by shifting the depletion region into an n type wide bandgap material. An in-house numerical model, which solves Poisson, continuity, and current equations for electrons and holes, is utilized for high precision in electrical and optical characterization of the detector. Composition and doping levels are optimized so that the collection of photo-generated carriers is not disturbed and the quantum efficiency is kept high.

A comprehensive model on field-effect pnpn devices (Z2-FET)

A comprehensive model for field-effect pnpn devices (Z2-FET) is presented. It is based on three current continuity equations coupled to two MOS equations. The model reproduces the characteristic S-shaped I-V curve when the device is driven by a current source. The negative resistance region at intermediate currents occurs as the center junction undergoes a steep transition from reverse to forward bias. Also playing a vital role are the mix and match of the minority carrier diffusion current and the generation recombination current. Physical insights to the key mechanisms at work are gained by regional approximations of the model, from which analytical expressions for the maximum and minimum voltages at the switching points are derived.

Electrical properties of zinc oxide – Tetracene heterostructures with different n-type ZnO films

Electrical properties of organic-inorganic p–n heterojunction structures with tetracene (Tc) and zinc oxide (ZnO) films were investigated. The ZnO films had different n-type carrier concentrations that varied from ∼1015 cm−3 to 1019 cm−3. Lower n-type ZnO layers resulted in decreased reverse currents in the ZnO:Al/ZnO/Tc/Au structures and in an improvement of their asymmetric properties. Experimentally determined energy level alignments at the ZnO/Tc interfaces were related to the electrical behavior of the structures. An improved rectification was associated with decreased generation-recombination currents at the ZnO/Tc interface due to an increased organic-inorganic interface energy gap. Current-voltage characteristics were analyzed by a differential approach. Electrical conduction mechanisms including bimolecular recombination as well as trap-filled limited conduction were identified in the investigated structures.

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.