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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.

The impact ionization characteristics of (Al x Ga1- x )0.52In0.48P have been studied comprehensively across the full composition range. Electron and hole impact ionization coefficients ( $\alpha $ and $\beta $ , respectively) have been extracted from avalanche multiplication and excess noise data for seven different compositions and compared to those of Al x Ga1- x As. While both $\alpha $ and $\beta $ initially decrease gradually with increasing bandgap, a sharp decrease in $\beta $ occurs in (Al x Ga1- x )0.52In0.48P when ${x} > 0.61$ , while $\alpha $ decreases only slightly. $\alpha $ and $\beta $ decrease minimally with further increases in ${x}$ and the breakdown voltage saturates. This behavior is broadly similar to that seen in Al x Ga1- x As, suggesting that it may be related to the details of the conduction band structure as it becomes increasingly indirect in both alloy systems.

Single photon avalanche diodes (SPADs) are key enabling technologies for a wide range of applications in the near-infrared wavelength range. Recently, AlAs0.56 Sb0.44 (hereafter AlAsSb) lattice-matched to InP has been demonstrated for extremely low excess noise avalanche photodiodes (APDs) due to its large disparity between electron and hole ionization coefficients ( $\alpha $ and $\beta $ respectively). The $\alpha /\beta $ ratio also plays a role in Geiger mode operation as it affects the avalanche breakdown probability and hence detection efficiency. In this work, we theoretically investigate the performance of AlAsSb based SPADs. The probability of breakdown for electron-initiated Geiger mode operation increases more sharply with multiplication region width due to progressively more dissimilar ionization coefficients. In comparison with other common avalanche materials, such as InAlAs, InP and Si, our result also suggests that SPADs based on AlAsSb have a sharper breakdown probability than the other three materials under similar low overbias ratio. The calculated breakdown probability of 0.81 in AlAsSb is 0.18 and 0.28 higher than that of InAlAs/Si and InP respectively at 5% overbias ratio and with avalanche region width of 1500 nm.

Photoluminescence (PL) and Raman spectra of GaAs1-xBix samples grown at different rates (0.09 to 0.5 µm/h) were investigated. The PL peak wavelength initially redshifted with the increase of growth rate and reached the longest wavelength (1158 nm) for sample grown at 0.23 µm/h. This is followed by PL peak wavelength blueshift for higher growth rates. The Raman data show peaks at 162, 228, 270, and 295 cm-1 which can be attributed to GaAs like phonons. GaBi like vibrational modes were also observed at 183 and 213 cm-1. However, the intensity of Bi induced phonons is significantly weaker compared to GaAs due to low concentration of Bi compared to As and thin GaAs1-xBix epilayer. The PL data and GaAs transverse optical (TO) to longitudinal optical (LO) phonons intensity ratio indicate that Bi concentration is highly dependent on the growth rate and the highest Bi concentration was obtained by sample grown at 0.23 µm/h. It is found that the full-width-at-half-maximum (FWHM) of GaAs LO mode increases significantly for samples grown at high growth rates suggesting crystal quality degradation due to lack of surfactant effects.

The research was conducted to determine with the title “Effect of Different Levels of Tapioca (Manihot esculenta) as a Fat Replacer in low Fat Probiotic Ice Cream” to develop suitable technology for the preparation of fat replacer in low fat probiotic ice cream, to access the feasibility of using four levels (5, 10, 15 and 20%) of tapioca (Manihot esculenta) with 1, 2 and 3% of L. Casei. Total 12 treatment combination was used in this study as T1L1(5% Tapioca + 1% L. Casei), T1L2(5% Tapioca + 2%L. Casei), T1L3(5% Tapioca + 3% L. Casei), T2L1(10% Tapioca + 1% L. Casei), T2L2(10% Tapioca + 2% L. Casei), T2L3(10% Tapioca + 3% L. Casei), T3L1(15% Tapioca + 1% L. Casei), T3L2(15% Tapioca + 2% L. Casei), T3L3(15% Tapioca + 3% L. Casei), T4L1(20% Tapioca + 1% L. Casei), T4L2(20% Tapioca + 2% L. Casei) and T4L3(20% Tapioca + 3% L. Casei) and all were replicated 4 times. The highest average value of colour and appearance score was obtained in the treatment T1L3 5% Tapioca + 3% L. casei (8.72). The highest average value of body and texture score was obtained in the treatment T1L3 5% Tapioca + 3% L. casei (8.04). The highest average value of flavor and taste score was obtained in the treatment T1L3 5% Tapioca + 3% L. casei (8.00). The highest average value of overall acceptability score content was obtained in the treatment T1L3 5% Tapioca + 3% L. casei (8.12). the highest average value of melting score was obtained in the treatment T4L3 20% Tapioca + 3% L. casei (8.52). the highest average value of over run was obtained in the treatment T1L1 5% Tapioca + 1% L. casei (71.80).

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.

The well-known analytical formula for the excess noise factor associated with avalanche photodiodes (APDs), developed by R. J. McIntyre in 1966, assumes the injection of either an electron or a hole at the edge of the APD's avalanche region. This formula is based on the statistics of the probabilities of carriers gaining and losing energy subject to high electric fields. However, this analytical formula, is not applicable in cases when photons are absorbed inside the avalanche region (even though the physics of the high field transport remains the same), and its use may severely underestimate or overestimate the actual excess noise factor depending on the absorption profile and the hole-to-electron ionization coefficient ratio, k . Here, an easy-to-use exact analytical formula is derived for the excess noise factor of APDs while taking into account a mixed-carrier initiated avalanche multiplication process, which is triggered by a parent electron-hole pair at an arbitrarily specified location within the multiplication region. The derivation relies on analytically solving a special case of a previously reported recursive integral equations [Hayat et al. , IEEE Trans. Electron Devices, vol. 39, no. 3, pp. 546–552, Mar. 1992.], and the result matches the formula reported by McIntyre in 1999 using a different and limited technique. In addition, an expression for the excess noise factor is presented in the case when the location of the parent electron-hole pair within the multiplication region obeys an arbitrary exponential distribution. The results show that in contrast to the case of edge parent-electron injection, when mixed injection is allowed even a small level of hole ionization (e.g., small k ∼ 0.0001) causes the excess noise factor to increase dramatically, depending on the absorption profile as it ranges from narrow to flat within the multiplication region. The theoretical results are validated against experimental results for Si APDs.

The optimization of thermophotovoltaic (TPV) cell efficiency is essential since it leads to a significant increase in the output power. Typically, the optimization of In0.53Ga0.47As TPV cell has been limited to single variable such as the emitter thickness, while the effects of the variation in other design variables are assumed to be negligible. The reported efficiencies of In0.53Ga0.47As TPV cell mostly remain 0.53Ga0.47As TPV cell using the real coded genetic algorithm (RCGA) at various radiation temperatures. RCGA was developed using Visual Basic and it was hybridized with Silvaco TCAD for the electrical characteristics simulation. Under radiation temperatures from 800 to 2000 K, the optimized In0.53Ga0.47As TPV cell efficiency increases by an average percentage of 11.86% (from 8.5 to 20.35%) as compared to the non-optimized structure. It was found that the incorporation of a thicker base layer with the back-barrier layers enhances the separation of charge carriers and increases the collection of photo-generated carriers near the band-edge, producing an optimum output power of 0.55 W/cm2 (cell efficiency of 22.06%, without antireflection coating) at 1400 K radiation spectrum. The results of this work demonstrate the great potential to generate electricity sustainably from industrial waste heat and the multi-dimensional optimization methodology can be adopted to optimize semiconductor devices, such as solar cell, TPV cell and photodetectors.

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.

Photoluminescence (PL) and Raman studies were carried out to investigate the effect of growth rate on $\mathrm{GaAs}_{1-\mathrm{x}}\mathrm{sBi}_{\mathrm{x}}$ alloys. The samples were grown between 0.09 and 0.5 $\mu\mathrm{m}/\mathrm{hour}$ , At room temperature, the lowest PL peak energy (1.07 eV) was obtained by sample grown at 0.23 $\mu\mathrm{m}/\mathrm{hour}$ . Samples grown at lower and higher than 0.23 $\mu\mathrm{m}/\mathrm{hour}$ showed PL peak energy redshift and blueshift, respectively. Raman data show peaks at 162, 228, 270 and 295 cm−1which correspond to the GaAs like phonons. The GaBi like phonons were also observed at 183 and 213 cm−1but their intensity are significantly weaker compared to GaAs like phonons. PL and Raman data show that Bi incorporation into GaAs lattice is dependent on the growth rate and in this study, the highest Bi concentration was obtained for sample grown at 0.23 $\mu \mathrm{m}/\mathrm{hour}$ .

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.

A four-parameter Weibull-Fréchet (WF) distribution function has been introduced in the random path length (RPL) model for nonlocal modelling of soft-threshold ionisation in semiconductors. The WF function has been demonstrated to be capable of reproducing the realistic probability distribution function (PDF) of electron and hole ionisation path lengths extracted from full band Monte Carlo (FBMC) transport simulations of bulk GaAs. The electron-initiated multiplication in GaAs avalanche photodiodes (APDs) calculated by the WF-RPL model is in excellent agreement with the results from FBMC. The predicted excess noise factor is closer to that of FBMC as compared to the hard threshold RPL model. The advantage of this improved RPL model as a tool for predicting the PDF of electron and hole ionisation path lengths in AlAs0.56Sb0.44 from the experimentally measured avalanche gain and noise has been analysed. The electron ionisation path length PDF of AlAs0.56Sb0.44 has a unique feature of two decay rates with a narrow full width at half maximum and a long tail. The extremely low hole ionisation coefficient in AlAs0.56Sb0.44 is found with a PDF of ionisation path length spanning over 50 µm at an electric field of 600 kVcm−1, supporting the very low hole feedback ionisation in AlAs0.56Sb0.44 APDs. The combination of the detailed and peaked electron’s ionisation path length PDF and of the broad hole’s ionisation path length PDF is responsible for the extremely low avalanche noise in the 1.55 µm thick AlAs0.56Sb0.44 APDs.

Mean-gain and excess-noise measurements are presented for a 350 × 350 μm2 P+/N-well/P-sub and a 270 × 270 μm2 N-well/P-sub avalanche photodetectors fabricated using 0.13-μm CMOS technology. The active area of the P+/N-well/P-sub device was divided into multiple subsections to decrease transit time and increase speed. For the P+/N-well structure, remarkably low excess-noise factors of 4.1 and 4 were measured at a mean gain of 16 corresponding to a k value of approximately 0.1, using a 542 (633) nm laser. For a variant N-well/P-sub structure, excess-noise factors of 6.5 and 6.2 were measured at a mean-gain of 16 corresponding to a k value of approximately 0.3. The proposed CMOS APDs with high gain, low noise, low avalanche breakdown voltage (below approximately 12 V) and low dark-currents (approximately nA) would be attractive for low-cost optical receivers in visible-light communication systems.

The objective of this special issue is to document the current state-of-the-art in the area of Optical Detectors and highlight recent progress and trends in innovative optical detector technology and its applications. This issue combines 11 invited and 21 contributed papers, authored byworld-renowned research groups and promising scientists from around the world. The invited papers present extended reviews on recent progress and significant perspectives on future research directions. They cover lownoise linear-mode avalanche photodiodes (APDs) for fiber optic communications, single photon APDs (SPADs) and Si SPAD arrays for photon counting imagers, hybrid integration technologies, waveguide APDs, lowcapacitance nano-photodetector, integrated photodetectors for coherent receivers, and high-speed uni-traveling carrier (UTC) photodiodes (PDs) for THz applications. The contributed papers cover a broad variety of key research areas and emerging technologies in optical detectors including graphene-based detectors, plasmonic structures for current enhancement, phototransistors, and UTC-type PDs on silicon-on-insulator waveguide as well as a UTC PD with type II hybrid absorber. Several papers describe advances in SPADs and CMOS SPAD arrays for UV and visible detection and four papers cover quantum well and quantum dot devices. This special issue also illustrates a wide range of optical detector technology applications including UV, visible, and IR imaging, fiber optic communications, microwave and THz analog applications, and quantum communications. Furthermore, this special issue covers a range of advances on theory and simulation, design and fabrication, and optical detector characterization methodologies.

InAsBi dilute alloys are potential new candidates for the improvement of infrared optoelectronic devices such as photodetectors or lasers. In this work, InAsBi/InAs superlattices (SLs) with Bi contents ranging between 1 and 3% were grown by molecular beam epitaxy with different Bi fluxes and growth temperatures to analyze Bi segregation by cross sectional transmission electron microscopy techniques. Bi segregation profiles have been described layer-by-layer using a three-layer fluid exchange mechanism, extracting the values of the As/Bi exchange energies (E1, 1.26 ± 0.01 eV and E2, 1.36 ± 0.02 eV). A relationship to calculate the activation energies for exchange from the binding energies in III–V alloys is proposed, which would allow predicting them for other hitherto unknown compounds.

GaAsBi light emitting diodes containing ∼6% Bi are grown on GaAs substrates. Good room-temperature electroluminescence spectra are obtained at current densities as low as 8 Acm − 2. Measurements of the integrated emitted luminescence suggest that there is a continuum of localised Bi states extending up to 75 meV into the bandgap, which is in good agreement with previous photoluminescence studies. X-ray diffraction analysis shows that strain relaxation has probably occurred in the thicker samples grown in this study.

The dark current characteristics of two series of bulk GaAsBi p-i-n diodes are analysed as functions of temperature and band gap. Each temperature dependent measurement indicates that recombination current dominates in these devices. The band gap dependence of the dark currents is also consistent with recombination dominated current for the devices grown at a common growth temperature, indicating that the presence of Bi does not directly adversely affect the dark currents. However, the devices grown at different growth temperatures exhibit a faster increase in dark current with decreasing device band gap, suggesting that a reduced growth temperature causes a reduction in minority carrier lifetime.

Dilute bismide III-V semiconductors have many unique properties and have been extensively investigated in recent decades. As the development of material research has progressed, some promising dilute bismide devices have been explored. Incorporation of a small amount of Bi in III-V host materials results in a large band-gap narrowing, which makes dilute bismides potential candidates in long-wavelength photodetectors. In this chapter, we review recent progress on GaAsBi, InAsBi, InSbBi, and InGaAsBi photodetectors, as well as GaAsBi and InGaAsBi THz photoconductive detectors. Some preliminary demonstrations and detector properties have been reported on these dilute bismide photodetectors, while the material quality still needs to be improved and the specific detector properties of dilute bismides still need more understanding.

A comprehensive assessment of the nature of the distribution of sub band-gap energy states in bulk GaAsBi is presented using power and temperature dependent photoluminescence spectroscopy. The observation of a characteristic red-blue-red shift in the peak luminescence energy indicates the presence of short-range alloy disorder in the material. A decrease in the carrier localisation energy demonstrates the strong excitation power dependence of localised state behaviour and is attributed to the filling of energy states furthest from the valence band edge. Analysis of the photoluminescence lineshape at low temperature presents strong evidence for a Gaussian distribution of localised states that extends from the valence band edge. Furthermore, a rate model is employed to understand the non-uniform thermal quenching of the photoluminescence and indicates the presence of two Gaussian-like distributions making up the density of localised states. These components are attributed to the presence of microscopic fluctuations in Bi content, due to short-range alloy disorder across the GaAsBi layer, and the formation of Bi related point defects, resulting from low temperature growth.

Multiplication and avalanche excess noise measurements have been undertaken on a series of AlInP homo-junction p-i-n and n-i-p diodes with $i$ region widths ranging from 0.04 to 0.89 $\mu \text{m}$ , using 442 and 460 nm wavelength light. Low dark currents of $^{\mathrm {-2}}$ at 95% of breakdown voltage were obtained in all the devices because of its wide bandgap and there was no tunneling dark current present even at high fields >1000 kV/cm. For a given multiplication factor, the excess noise decreased as the avalanche width decreased due to the dead-space effect. Using 460 nm wavelength light, measurements showed that a separate absorption multiplication avalanche photodiode with a nominal multiplication region width of 0.2 $\mu \text{m}$ had an effective $k$ (hole to electron ionization coefficient ratio) of $\sim 0.3$ .

A series of GaAsBi/GaAs multiple quantum well p–i–n diodes were grown by molecular beam epitaxy. Nomarski images showed evidence of sub-surface damage in each diode, with an increase in the cross-hatching associated with strain relaxation for the diodes containing more than 40 quantum wells. X-ray diffraction ω–2θ scans of the (004) reflections showed that multiple quantum well regions with clearly defined well periodicities were grown. The superlattice peaks of the diodes containing more than 40 wells were much broader than those of the other diodes. The photoluminescence spectra showed a redshift of 56meV and an attenuation of nearly two orders of magnitude for the 54 and 63 well diodes. Calculations of the quantum confinement and strain induced band gap modifications suggest that the wells in all diodes are thinner than their intended widths and that both loss of quantum confinement and strain probably contributed to the observed redshift and attenuation in the 54 and 63 well diodes. Comparison of this data with that gathered for InGaAs/GaAs multiple quantum wells, suggests that the onset of relaxation occurs at a similar average strain–thickness product for both systems. Given the rapid band gap reduction of GaAsBi with Bi incorporation, this data suggests that GaAsBi is a promising photovoltaic material candidate.

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.

The demonstration of a prototype avalanche photodiode with a staircase band profile suggests that such devices may ultimately become a viable alternative to photomultiplier tubes in the infrared.

The application of visible light communication (VLC) systems is to transmit data while maintaining efficient and good quality illumination service. In order to meet standard lighting requirements when multi-colored modulation techniques are used, such as color shift keying (CSK), the color fluctuation becomes a relevant issue. This paper presents a multi- primary (multi-color) modulation technique which provides reliable data transmission while keeping a strong constraint on the light color illuminated by every symbol of the modulation alphabet. The number of possible primary color combinations that ensure white light are calculated for a given set of multi-color light sources. The system performance in terms of bit error rate for different constellation is evaluated and compared against other multi-color VLC schemes in the literature, considering a range of channel impairments due to the optical front-end components.

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.

We demonstrate an ${\rm Al}_{0.52}{\rm In}_{0.48}{\rm P}$ homo-junction Separate Absorption Multiplication Avalanche Photodiode as a detector with narrow spectral response in the blue-green part of the optical spectrum. Due to its wide band-gap, this device has a dark current density of ${\rm cm}^{-2}$ at 99.9% of the breakdown voltage at room temperature. This device has a peak responsivity at 483 nm of 0.15 A/W when punched-through and is capable of an avalanche gain higher than 100.

This paper presents a new color shift keying (CSK) modulation format for wireless visible light communication (VLC), based on four colors instead of the three colors used in the existing IEEE 802.15.7 CSK physical layer standard. The new four color system uses a novel intensity modulation and direct detection approach to realize a four-dimensional signaling scheme that uses the available color and signal spaces efficiently. The bit error rate evaluation of both the existing and proposed system shows that the new four color scheme achieves a significant 4.4-dB electrical SNR gain over the three color scheme for an additive white Gaussian noise channel. The performance of existing and proposed CSK systems is examined over a range of dispersive optical wireless channels including the channel crosstalk and insertion losses, which reveals that the four color CSK scheme is more power efficient and reliable than the three color scheme for a particular amount of delay spread that the optical wireless channel may have.

The structural and optical properties of GaAs1−xBix alloys for x up to 0.108 have been investigated by high resolution X-ray diffraction and photoluminescence (PL). At room temperature (RT), the PL intensity of the GaAs0.97Bi0.03 sample was found to be ∼300 times higher than a GaAs control sample grown at the same temperature (400 °C). PL measurements carried out at 10 K show that when excitation power, Pex was increased from 0.11 to 1140 W cm−2, the PL peak energy blue-shifts by 80 meV while the full-width-at-half-maximum reduces from 115 to 63 meV. However, the PL peak emission energy becomes independent of the excitation power at RT. The results indicate the presence of localized energy states in the GaAs0.97Bi0.03 sample, which trap carriers at low temperatures and that the majority of the carriers become delocalized at RT. Furthermore, the temperature dependent PL also shows an S-shape behavior, which is a signature of localization effects. A theoretical model, which was derived by solving a rate equation was employed. The model successfully reproduces the observed S-shape behavior and the theory fits well with the experimental data. The RT band gap of GaAs1−xBix for x up to 0.108 has been plotted and compared with the literature.

100 nm thick GaAsBi layers were grown at a range of temperatures using both As 2 and As 4 . Measurements of Bi incorporation based on room temperature photoluminescence spectra indicate that the growth temperature dependence of Bi incorporation is the same for both As species and is invariant with respect to Bi flux; however, Bi incorporation saturates when the growth temperature is low enough for the Bi incorporation coefficient to reach unity. The As:Ga atomic flux ratios allowing significant Bi incorporation are coincident for both As species upon accounting for desorption of 50% of the incident As 4 atoms during GaAs growth. The Bi reconstruction lifetime at 415 °C was measured under overpressures of both As species and under vacuum. The lifetime is significantly longer than the monolayer growth time used in this work; however, results do show that As 2 is more aggressive at displacing Bi from a static surface than As 4 . The photoluminescence intensities of the samples grown in this work vary with Bi incorporation in accordance with current literature and appear to be independent of As species.

We report the evaluation of a molecular-beam epitaxy grown two-color photodetector for radiation thermometry. This two-color photodetector consists of two p+in+ diodes, an In0.53Ga0.25Al0.22As (hereafter InGaAlAs) p+in+ diode, which has a cutoff wavelength of 1180 nm, and an In0.53Ga0.47As (hereafter InGaAs) p+in+ diode with a cutoff wavelength of 1700 nm. Our simple monolithic integrated two-color photodetector achieved comparable output signal and signal-to-noise (SNR) ratio to that of a commercial two-color Si-InGaAs photodetector. The InGaAlAs and InGaAs diodes detect blackbody temperature as low as 275°C and 125°C, respectively, with an SNR above 10. The temperature errors extracted from our data are 4°C at 275°C for the InGaAlAs diode and 2.3°C at 125°C for the InGaAs diode. As a ratio thermometer, our two-color photodetector achieves a temperature error of 12.8°C at 275°C, but this improves with temperature to 0.1°C at 450°C. These results demonstrated the potential of InGaAlAs-InGaAs two-color photodetector for the development of high performance two-color array detectors for radiation thermometry and thermal imaging of hot objects.