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Avalanche photodiodes (APDs) are used in optical receivers of high-speed optical communication systems to improve signal-to-noise ratio over conventional photodiodes. Low excess noise characteristics are crucial for APDs to preserve the benefits associated with high internal gains. In this work, we presented room temperature data of avalanche gain and excess noise factors of Al0.85Ga0.15As0.56Sb0.44 APDs using pure and mixed carrier injection profiles. Using pure electron injection, the best possible excess noise performance for a given avalanche width was measured with an excess noise factor https://doi.org/10.15131/shef.data.15082455 )

Avalanche Photodiodes (APDs) are key semiconductor components that amplify weak optical signals via the impact ionization process, but this process’ stochastic nature introduces ‘excess’ noise, limiting the useful signal to noise ratio (or sensitivity) that is practically achievable. The APD material’s electron and hole ionization coefficients (α and β respectively) are critical parameters in this regard, with very disparate values of α and β necessary to minimize this excess noise. Here, the analysis of thirteen complementary p-i-n/n-i-p diodes shows that alloying GaAs with ≤ 5.1 % Bi dramatically reduces β while leaving α virtually unchanged—enabling a 2 to 100-fold enhancement of the GaAs α/β ratio while extending the wavelength beyond 1.1 µm. Such a dramatic change in only β is unseen in any other dilute alloy and is attributed to the Bi-induced increase of the spin-orbit splitting energy (∆so). Valence band engineering in this way offers an attractive route to enable low noise semiconductor APDs to be developed., An avalanche photodiode is an opto-electronic amplifier that uses impact ionization to provide enhanced sensitivity at the expense of excess noise. In this manuscript, the authors demonstrate that a small amount of Bismuth (Bi) in Gallium Arsenide (GaAs) avalanche photodiodes significantly reduces this excess noise.

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.

Avalanche photodiodes (APDs), and single photon avalanche diodes (SPADs), with InP avalanche regions and InGaAs absorption regions, are used for detecting weak infrared light at ∼1.55 μm wavelength. These devices are often cooled to below room temperature during operation yet both validated simulation models and impact ionization coefficients that accurately describe the avalanche characteristics of InP are lacking in the temperature range of interest (200 K to room temperature). In this article we present an accessible, validated temperature dependent simulation model for InP APDs/SPADs. The model is capable of simulating avalanche gain, excess noise, breakdown voltage, and impulse current at 150–300 K. Temperature dependent ionization coefficients in InP, which may be used with other APD/SPAD simulation models, are also presented. The data reported in this article is available from the ORDA digital repository (DOI: 10.15131/shef.data.c.4373006).

Fast, sensitive avalanche photodiodes (APDs) are required for applications such as high-speed data communications and light detection and ranging (LIDAR) systems. Unfortunately, the InP and InAlAs used as the gain material in these APDs have similar electron and hole impact ionization coefficients (α and β, respectively) at high electric fields, giving rise to relatively high excess noise and limiting their sensitivity and gain bandwidth product1. Here, we report extremely low excess noise in an AlAs0.56Sb0.44 lattice matched to InP. A deduced β/α ratio as low as 0.005 with an avalanche region of 1,550 nm is close to the theoretical minimum and is significantly smaller than that of silicon, with modelling suggesting that vertically illuminated APDs with a sensitivity of −25.7 dBm at a bit error rate of 1 × 10−12 at 25 Gb s−1 and 1,550 nm can be realized. These findings could yield a new breed of high-performance receivers for applications in networking and sensing.

This paper presents the electron and hole avalanche multiplication and excess noise characteristics based on bulk AlAs0.56Sb0.44 p-i-n and n-i-p homojunction diodes lattice matched to InP, with nominal avalanche region thicknesses of 0.6 -1.5 μm. From these, the bulk electron and hole impact ionization coefficients (α and β respectively), have been determined over an electric field range of 220-1250 kV/cm for α and from 360-1250 kV/cm for β for the first time. Excess noise characteristics suggest an β/α ratio as low as 0.005 for an avalanche region of 1.5 μm in this material, close to the theoretical minimum and significantly lower than AlInAs, InP, or even silicon. This material can be easily integrated with InGaAs for networking and sensing applications, with modeling suggesting that a sensitivity of -32.1 dBm at a bit-error rate (BER) of 1×10-12 at 10 Gb/s at 1550 nm can be realized. This sensitivity can be improved even further by optimizing the dark currents and by using a lower noise transimpedance amplifier.

InAs thermophotovoltaic (TPV) cells with external quantum efficiency at the peak wavelengths reaching 71% at low temperature and 55% at room temperature are reported, which are the highest values to date for InAs. The TPV exhibited 10% power conversion efficiency at 100 K cell temperature. The dark and light current-voltage characteristics were measured at different cell temperatures (100–340 K) in response to heat sources in the range 500–800 °C. The resulting dependences of the output voltage and current as well as the spectral response of the InAs TPV have been extensively characterized for waste heat recovery applications. The performance of these cells is strongly determined by the dark current which increases rapidly with increasing cell temperature originating from bandgap narrowing, which resulted in a reduction of open circuit voltage and output power.

Thin avalanche layers have been adopted to achieve low excess noise and high-gain bandwidth products in InP and InAlAs avalanche photodiodes. In this paper, we report the excess noise characterization in a series of $\text{Al}_{\mathbf{1{-}}{\boldsymbol x}}$ Ga $_{\boldsymbol{x}}$ As $_{\mathbf{0.56}}$ Sb $_{\mathbf{0.44}}$ ( $x\,= \,0,\,0.05$ , 0.1, 0.15) diodes with avalanche layer thickness of 110–116 nm. These alloys, lattice matched to InP, showed lower excess noise than InP and InAlAs. Dark current, most probably originating from surface leakage, was observed to be lower in composition with higher Ga concentration. Avalanche gain and excess noise measurements using lasers of 543 and 633 nm wavelengths indicated that at a given electric field, the electron ionization coefficient is larger than the hole ionization coefficient. Using the 543 nm laser, low excess noise data corresponding to an effective ionization coefficient ratio of $k\,= \,0.1$ in the conventional excess noise theory was measured in $\text{Al}_{\mathbf{1{-}}{\boldsymbol x}}$ Ga $_{\boldsymbol{x}}$ As $_{\mathbf{0.56}}$ Sb $_{\mathbf{0.44}}$ ( $x\,= \,0.05$ , 0.1, 0.15), although pure electron injection was not achieved. Our results demonstrated the potential of using $\text{Al}_{\mathbf{1{-}}{\boldsymbol x}}$ Ga $_{\boldsymbol{x}}$ As $_{\mathbf{0.56}}$ Sb $_{\mathbf{0.44}}$ ( $x\,= \,0.05$ , 0.1, 0.15) as replacement for InP and InAlAs for high speed and low excess noise avalanche photodiodes. The data reported in this paper is available from the ORDA digital repository ( https://doi.org/10.15131/shef.data.5155822 ).

AlAs0.56Sb0.44 is a promising avalanche material which can be grown lattice-matched to InP and therefore use InGaAs as the absorption region in a Separate Absorption and Multiplication APD (SAM-APD). The electron and hole ionisation coefficients in this material are very dissimilar and our experiments show that this leads to AlAs0.56Sb0.44 having the lowest excess noise performance of any InP based material system (F = 2.2 at M = 40) reported to date. Simulations suggest that operation at 1550 nm and 25 GB s-1 with a sensitivity of -25.7 dBm is possible in a normal incidence SAM-APD.

Indium Arsenide (InAs) infrared photodiodes provide high quantum efficiency in the wavelength range of 1.0-3.0 μm. Planar diode configuration has been adopted to reduce surface leakage. In this work, new fabrication procedures for planar InAs avalanche photodiodes (APDs) are reported. Beryllium (Be) ions were implanted into InAs at a relatively low energy of 34 keV. Effects of duration of post implant annealing on the electrical characteristics of InAs APDs were investigated. It was found that a combination of post implant annealing at 500 °C for 15 min and a shallow surface etch produces planar APDs with good characteristics (room temperature dark current density of 0.52 A/cm 2 at -0.2 V and external quantum efficiency of 51% at 1520 nm at -0.3 V). These represent a 3 times reduction in dark current and 1.4 times increase in responsivity, compared to earlier Be-implanted planar InAs APDs. The APDs' avalanche gain characteristics remain similar to those from earlier reports, with a gain of 4 at a relatively low operating bias of 5 V. This suggests the potential of integrating InAs APDs with low voltage readout integrated circuits (ROIC) for development of infrared imaging arrays. The data reported in this paper is available from the ORDA digital repository (DOI: 10.15131/shef.data.6955037).

We demonstrated that an InAs photodiode and a Quantum Dot Infrared Photodiode can be bonded to produce a hybrid broadband infrared photodetector. When cooled to 77 K the InAs photodiode can be used to detect wavelengths from visible to a cutoff wavelength of 3 µm while the Quantum Dot Infrared Photodiode detects wavelengths from 3 to 12 µm. The dark current and spectral response were measured on reference devices and bonded devices. Both sets of devices show similar dark current and spectral response, suggesting that no significant degradation of the devices after the bonding process.

An avalanche photodiode with a ratio of hole-to-electron ionization coefficients, k = 0, is known to produce negligible excess noise irrespective of the avalanche gain. The low noise amplification process can be utilized to detect very low light levels. In this work, we demonstrated InAs avalanche photodiodes with high external quantum efficiency of 60% (achieved without antireflection coating) at the peak wavelength of 3.48 µm. At 77 K, our InAs avalanche photodiodes show low dark current (limited by 300 K blackbody background radiation), high avalanche gain and negligible excess noise, as InAs exhibits k = 0. They were therefore able to detect very low levels of light, at 15-31 photons per 50 µs laser pulse at 1550 nm wavelength. These correspond to the lowest detected average power by InAs avalanche photodiodes, ranging from 19 to 40 fW. The measurement system’s noise floor was dominated by the pre-amplifier. Our results suggest that, with a lower system noise, InAs avalanche photodiodes have high potential for optical detection of single or few-photon signal levels at wavelengths of 1550 nm or longer.

Conventional thermal imaging cameras, based on focal-plane array (FPA) sensors, exhibit inherent problems: such as stray radiation, cross-talk and the calibration uncertainty of ensuring each pixel behaves as if it were an identical temperature sensor. Radiation thermometers can largely overcome these issues, comprising of only a single detector element\ud \ud that can be optimised and calibrated. Although the latter approach can provide excellent accuracy for single-point temperature measurement, it does not provide a temperature image of the target object. In this work, we present a micromechanical systems (MEMS) mirror and silicon (Si) avalanche photodiode (APD) based single-pixel camera, capable of producing quantitative thermal images at an operating wavelength of 1 μm. This work utilises a custom designed f-theta wide-angle lens and MEMS mirror, to scan +/− 30° in both x- and ydimensions, without signal loss due to vignetting at any point in the field of view (FOV). Our single-pixel camera is shown to perform well, with 3 °C size-of-source effect (SSE) related temperature error and can measure below 700 °C whilst achieving ± 0.5 °C noise related measurement uncertainty. Our measurements were calibrated and traceable to the International Temperature Scale of 1990 (ITS-90). The combination of low SSE and absence of vignetting enables quantitative temperature measurements over a spatial field with measurement uncertainty at levels lower than would be possible with FPA based thermal imaging cameras.

The usefulness of avalanche photodiodes (APDs) resides in their ability to produce internal gain via impact ionization without generating excessive noise. This process is stochastic and the gain values fluctuate around a mean value, giving rise to the so-called excess noise. In this work, we evaluate the gain fluctuations in APDs using a multi-channel analyzer (MCA). Two Al0.85Ga0.15As0.56Sb 0.44 APDs, one p-i-n and one n-i-p were used. Illuminated with a pulsed light source, the APDs were connected to a charge-sensitive amplifier, counting the number of charges created by each avalanche event initiated by the light pulse. The signal was subsequently sent to an MCA, recording the gain values and outputting a gain spectrum. Both APDs were investigated for mean gains up to ~ 9. For a given mean gain, the gain distribution for the n-i-p diode was found to be significantly broader than for the p-i-n diode, as expected from the excess noise values previously measured in those devices. The coefficient of variance (CoV), defined as the ratio of standard deviation to mean value of the gain peaks, was found to be low for the p-i-n APD, consistent with the low excess noise values in this material. For higher mean gain values, the CoV of the n-i-p APD gave higher values than for the p-i-n APD, again corroborating the conventional excess noise measurements.

Avalanche photodiodes are widely used in optical receivers for high-speed communication systems. We have been studying the material AlGaAsSb (lattice-matched to InP substrates) experimentally in recent years, evaluating its potential as an alternative avalanche material for these avalanche photodiodes. Our experimental studies cover key characteristics relevant to high-speed avalanche photodiodes. The data obtained show that the material AlGaAsSb has higher gain-bandwidth product, lower excess noise factors, and weaker temperature dependence, compared to current avalanche materials such as InP and InAlAs.

The Bi content in GaAs/GaAs1 − xBi x /GaAs heterostructures grown by molecular beam epitaxy at a substrate temperature close to 340 °C is investigated by aberration-corrected high-angle annular dark-field techniques. The analysis at low magnification of high-angle annular dark-field scanning transmission electron microscopy images, corroborated by EDX analysis, revealed planar defect-free layers and a non-homogeneous Bi distribution at the interfaces and within the GaAsBi layer. At high magnification, the qHAADF analysis confirmed the inhomogeneous distribution and Bi segregation at the GaAsBi/GaAs interface at low Bi flux and distorted dumbbell shape in areas with higher Bi content. At higher Bi flux, the size of the Bi gathering increases leading to roughly equiaxial Bi-rich particles faceted along zinc blende {111} and uniformly dispersed around the matrix and interfaces. FFT analysis checks the coexistence of two phases in some clusters: a rhombohedral pure Bi (rh-Bi) one surrounded by a zinc blende GaAs1 − xBi x matrix. Clusters may be affecting to the local lattice relaxation and leading to a partially relaxed GaAsBi/GaAs system, in good agreement with XRD analysis.

We report an evaluation of an epitaxially grown uncooled InAs photodiode for the use in radiation thermometry. Radiation thermometry measurements was taken using the photodiode covered blackbody temperatures of 50 °C–300 °C. By determining the photocurrent and signal-to-noise ratio, the temperature error of the measurements was deduced. It was found that an uncooled InAs photodiode, with the peak and cutoff wavelengths of 3.35 and 3.55 $\mu \text{m}$ , respectively, measured a temperature of 50 °C, with an error of 0.17 °C. Many plastics have $C$ – $H$ molecular bond absorptions at 3.43 $\mu \text{m}$ and hence radiate thermally at this wavelength. Our results suggest that InAs photodiodes are well suited to measure the temperature of plastics above 50 °C. When tested with a narrow bandpass filter at 3.43 $\mu \text{m}$ and blackbody temperatures from 50 °C–300 °C, the InAs photodiode was also found to produce a higher output photocurrent, compared with a commercial PbSe detectors.

Be ion implantation and annealing conditions were optimized to demonstrate an effective method for selective area p-type doping in InAs. Optimized implantation and annealing conditions were subsequently utilized to produce planar InAs diodes. The Be implanted planar diodes had a superior dynamic resistance-area product and comparable dark current with n-i-p InAs mesa diodes when operated at low temperatures.

Waveguide InGaAs/InAlAs avalanche photodiodes (APDs) with high bandwidths (>40 GHz) and low dark current (

With increasing interest over the past decade in space-related remote sensing and communications using near-infrared (NIR) wavelengths, there is a need for radiation studies on NIR avalanche photodiodes (APDs), due to the high radiation environment in space. In this work, we present an experimental study of proton radiation effects on performance parameters of InAs APDs, whose sensitivity extends from visible light to ~3.5 μm. Three irradiation energies (10.0, 31.4, and 58.8 MeV) and four fluences (10sup9/supto 10sup11/supp/cmsup2/sup) were used. At the harshest irradiation condition (10.0 MeV energy and 10sup11/supp/cmsup2/supfluence) the APDs' avalanche gain and leakage current showed a measurable degradation. However, the responsivity of the APDs was unaffected under all conditions tested. The data reported in this article are available from the figshare digital repository (DOI: https://dx.doi.org/10.15131/shef.4560562).

Accurate quantitative temperature measurements are difficult to achieve using focal-plane array sensors. This is due to reflections inside the instrument and the difficulty of calibrating a matrix of pixels as identical radiation thermometers. Size-of-source effect (SSE), which is the dependence of an infrared temperature measurement on the area surrounding the target area, is a major contributor to this problem and cannot be reduced using glare stops. Measurements are affected by power received from outside the field-of-view (FOV), leading to increased measurement uncertainty. In this work, we present a micromechanical systems (MEMS) mirror based scanning thermal imaging camera with reduced measurement uncertainty compared to focal-plane array based systems. We demonstrate our flexible imaging approach using a Si avalanche photodiode (APD), which utilises high internal gain to enable the measurement of lower target temperatures with an effective wavelength of 1 µm and compare results with a Si photodiode. We compare measurements from our APD thermal imaging instrument against a commercial bolometer based focal-plane array camera. Our scanning approach results in a reduction in SSE related temperature error by 66 °C for the measurement of a spatially uniform 800 °C target when the target aperture diameter is increased from 10 to 20 mm. We also find that our APD instrument is capable of measuring target temperatures below 700 °C, over these near infrared wavelengths, with D* related measurement uncertainty of ± 0.5 °C.

Avalanche photodiodes (APDs) with thin avalanche regions have shown low excess noise characteristics and high gain-bandwidth products, so they are suited for long-haul optical communications. In this work, we investigated how carrier injection profile affects the avalanche gain and excess noise factors of Al5787318).

Avalanche photodiodes (APDs) with thin avalanche regions have shown low excess noise characteristics and high gain-bandwidth products, so they are suited for long-haul optical communications. In this work, we investigated how carrier injection profile affects the avalanche gain and excess noise factors of Al0.85Ga0.15As0.56Sb0.44 (lattice-matched to InP substrates) p-i-n and n-i-p diodes with total depletion widths of 145-240 nm. Different carrier injection profiles were achieved by using light with wavelengths of 420, 543 and 633nm. For p-i-n diodes, shorter wavelength light produces higher avalanche gains for a given reverse bias and lower excess noise factors at a given gain, compared to longer wavelength light. Thus, using 420 nm light on the p-i-n diodes, corresponding to pure electron injection conditions, gave the highest gain and lowest excess noise. In n-i-p diodes, pure hole injection yields significantly lower gain and higher excess noise, compared to mixed carrier injection. These show that the electron ionization coefficient, α, is higher than the hole ionization coefficient, β. Using pure electron injection, excess noise factor characteristics with effective ionization ratios, keff, of 0.08-0.1 were obtained. This is significantly lower than those of InP and In0.52Al0.48As, the commonly used avalanche materials combined with In0.53Ga0.47As absorber. The data reported in this paper is available from the ORDA digital repository (DOI: 10.15131/shef.data.5787318).

Avalanche gain and breakdown voltage in most wide bandgap semiconductor materials are dependent on temperature and most instruments utilizing APDs rely on temperature stabilization or voltage compensation circuitry to maintain a constant avalanche gain. The complexity in operation circuitry can be reduced by incorporating material with inherently superior temperature stability in its avalanche gain and breakdown voltage. In state of the art APDs, the temperature dependence of avalanche breakdown voltage is quantified by the temperature coefficient of avalanche breakdown, Cbd. We report on the temporal and temperature stability of avalanche gain and breakdown voltage of 100 nm thick avalanche layers of Al0.85Ga0.15As0.56Sb0.44 (AlGaAsSb). The Cbd (1.60 mV/K) is smaller compared to state of art InP and InAlAs APDs for similar avalanche layer thickness. The temporal stability of avalanche gain for the AlGaAsSb APD was also evaluated in temperature ranges of 294 K to 353 K. The APD was biased at room temperature gain of 10 and maximum fluctuation of ±0.7% was recorded at 294 K which increases to ±1.33% when the temperature was increased to 353K. The promising temperature stability of gain indicates the potential of AlGaAsSb lattice matched to InP in achieving higher tolerance to temperature fluctuations and reduction of the operational complexity of circuitry. The dark currents are robust and do not show significant thermal degradation after gain measurements at elevated temperatures.

We realize fast, efficient and small footprint niobium nitride superconducting nanowire single photon detectors atop of photonic waveguides. By reducing the bias current of the nanowire, in order to break the superconductivity and trigger a detection event, more than one photon needs to be absorbed in a localized section of the wire within a very short time delay (hot-spot relaxation time), making such devices promising also for multiphoton sensing applications. We adopt a near-infrared pump-probe technique in a cryogenic environment to investigate the bias current dependence of the hot-spot relaxation time. A minimum relaxation time of (22 ± 1) ps is obtained when applying a bias current of 50% of the switching current at a bath temperature of 1.7K. Our study reveals a strong increase of the picosecond relaxation time with increasing bias current. We further adopt the same technique for determining the multi-photon detection regimes of the detector, which are in agreement with standard quantum detector tomography. In this context, we introduce a practical model and reconstruction method for determining the detector sensitivity regimes. Our work provides a complete description of the detector working operation in both number photon threshold sensitivity and time-delay sensitivity. The results allow for implementing on-chip measurement architectures for the characterization of weak classical light emitters and fast single photon sources with only one detector, driven at different biasing currents, with a drastic reduction of the time uncertainty limitations of typical correlation measurement systems.

Nanophotonic integrated circuits are emerging as a promising platform for quantum photonics. A key building block are waveguide integrated detectors with superior performance. Detectors based on superconductor nanowires (SNSPDs) attached to optical waveguides have been shown to provide high efficiency and good timing performance, as well as broad bandwidth. To move towards applications in high bandwidth quantum communication and processing, ultrafast single-photon detectors with high efficiency are needed. The speed of meander type SNSPDs is limited because the required high absorption efficiency necessitates long nanowires deposited on top of the waveguide. This enhances the kinetic inductance and makes the detectors slow. We overcome this problem by aligning the nanowire perpendicular to the waveguide to realize devices with a length below 1 µm. By integrating the nanowire into a photonic crystal cavity, we recover high absorption efficiency, thus enhancing the detection efficiency by more than an order of magnitude. Our cavity enhanced superconducting nanowire detectors are fully embedded in silicon nanophotonic circuits and efficiently detect single photons at telecom wavelengths. The detectors possess sub-nanosecond decay (~ 120 ps) and recovery times (~ 510 ps), and thus show potential for GHz count rates at low timing jitter (~ 32 ps).

Efficiency of photoconductive detectors is limited by the bulk optical properties of photoconductive materials. The absorption length is on the order of several hundred nanometers, which limits the device thickness. Optical absorption however in the photoconductive layer can be modified substantially by using the concept of hybrid cavity, which consists of nanoantennas and a Distributed Bragg Reflector. A hybrid cavity containing a GaAs photoconductive layer of just 50 nm can be used to absorb >75% of incident photons by trapping the light within the cavity. We will discuss an intuitive model, which describes the dependence of the optimum operation wavelength on the cavity thickness. We will also show that the nanoantenna size is a critical parameter, small variations of which lead to both wavelength shifting and reduced absorption in the cavity. This behavior suggests that impedance matching is key for achieving efficient absorption in the hybrid cavities.

Although ZnO and its related heterostructures are really attractive for their potential application in optoelectronics, their developments have been limited by the p-type doping issue. Here, we will show why ZnO properties are also very attractive for unipolar structures, only dealing with electrons, and how the material quality has been improved to reach these devices requirements. First, the benefit of homoepitaxy through material quality improvement is presented. We will show that molecular beam epitaxy allows getting defect density, surface roughness, and residual doping, comparable to the state-of-the-art of GaAs. Moreover, (Zn,Mg)O alloy could be used to fabricate heterostructures with very good optical and transport properties. In the second part, we will give a brief overview of the main transport results, especially bidimensional electron gas, reported in the literature. Few examples of possible applications will also be addressed. Then, we will focus on the potentialities of nonpolar ZnO heterostructures for unipolar devices based on intersubband transitions. Once the advantages of using ZnO for TeraHertz quantum cascade laser discussed, we will show that the structural properties of the ZnO/(Zn,Mg)O heterostructures fulfill the requirements of these devices operation. Moreover, we will finish with absorption measurements clearly showing intersubband transitions in agreement with the light polarization selection rule. The strong influence of physical parameters, like doping level, on the energy of these kind of transitions will also be discussed. This work was funded by EU commission under the H2020 FET-OPEN program; project “ZOTERAC” FET-OPEN 6655107.

Colloidal quantum dots (CQD) attract much interest for optoelectronic applications, as potentially low-cost alternatives to epitaxial materials. In particular, in the mid-IR spectral range, CQD based on the zinc-blend mercury chalcogenides, Hg (S, Se, Te), lead efforts to create mid-IR technologies with solutions based materials. HgTe CQD with their tunable bandgap above 3 microns show promise as mid-IR detectors at a lower cost than existing HgCdTe (MCT) detectors. Progress towards the manufacture of mid-infrared cameras, improved sensitivity of PV devices, and new modalities, will be reviewed. HgS and HgSe CQDs also allow photodetection in the mid-IR because they are stably n-doped in ambient conditions, and they show an intense intraband transitions tunable in the mid-IR. Intraband CQDs is therefore another promising approach that broadens the types of materials considered. For both approaches, some of the challenges are similar, as one needs to develop tightly size-controlled colloidal quantum dots, and an interfacial chemistry that maximizes mobility and carrier lifetime, yet allows for controlling the doping.

There has been significant progress on the development of Type II superlattice detectors in the past 15 years. As we have progressed in advanced heterostructure engineering of the devices, it has also provided insight into some of the challenges associated with the superlattices. In this talk, I will discuss some of our recent results on unipolar barrier detectors. I will also discuss some of the fundamental challenges that need to be addressed for the superlattice detectors such as vertical transport and surface passivation. I will also present some interesting problems including superlattice based avalanche photodiodes and the growth of metamorphic InAsSb absorbers.

The ability to integrate electronics with Nanocrystals (NCs) allows utilizing their unique properties for a future optoelectronic device. Combing top down approach using self-assembled hybrid organic-NCs systems, with bottom up components can revolutionize devices in future. In my talk I will present an ultra-high light sensing device based on InAs NCs acting as an optical gate to high electron mobility transistor (HEMT) device. Using a very narrow channel the device quantum efficiency is high as 106V/W, while the single to noise ratio (SNR) enables high sensitivity photon detection. In addition a side gate detector will be present showing enhancement in the sensitivity for light and gas detection. The same concept can be used to develop tunable, simple and flexible detector for the IR range printing semiconducting/conducting carbon nanotubes layer mixed with doped semiconductor nanocrystals.

InAs avalanche photodiodes (APDs) can be designed such that only electrons are allowed to initiate impact ionization, leading to the lowest possible excess noise factor. Optimization of wet chemical etching and surface passivation produced mesa APDs with bulk dominated dark current and responsivity that are comparable and higher, respectively, than a commercial InAs detector. Our InAs electron-APDs also show high stability with fluctuation of ~0.1% when operated at a gain of 11.2 over 60 s. These InAs APDs can detect very weak signal down to ~35 photons per pulse. Fabrication of planar InAs by Be implantation produced planar APDs with bulk dominated dark current. Annealing at 550 °C was necessary to remove implantation damage and to activate Be dopants. Due to minimal diffusion of Be, thick depletion of 8 μm was achieved. Since the avalanche gain increases exponentially with the thickness of avalanche region, our planar APD achieved high gain > 300 at 200 K. Our work suggest that both mesa and planar InAs APDs can exhibit high gain. When combined with a suitable preamplifier, single photon detection using InAs electron-APDs could be achieved.