Generation-recombination Mechanisms Research Articles

Research on Electro-Optical Characteristics of Infrared Detectors with HgCdTe Operating at Room Temperature.

This paper presents a thorough analysis of the current-voltage characteristics of uncooled HgCdTe detectors optimized for different spectral ranges. HgCdTe heterostructures were grown by means of metal-organic chemical vapor deposition (MOCVD) on GaAs substrates. The obtained detector structures were measured using a Keysight B1500A semiconductor device analyser controlled via LabVIEW for automation. The experimental characteristics were compared with numerical calculations performed using the commercial platform SimuAPSYS (Crosslight). SimuAPSYS supports detector design and allows one to understand different mechanisms occurring in the analysed structures. The dark current density experimental data were compared with theoretical results at a temperature of 300 K for short, medium, and long wavelength infrared ranges. The dark current density of detectors optimized for different wavelengths was determined using various generation-recombination mechanisms. Proper matching between experimental and theoretical data was obtained by shifting the Shockley-Read-Hall carrier lifetime and the Auger-1 and Auger-7 recombination rates. Exemplary spectral responses were also discussed, giving a better insight into detector performance. The matching level was proven with a theoretical evaluation of the zero-bias dynamic resistance-area product (R0A) and the current responsivity of the designed detectors.

Calculation of Minority Carriers’ Lifetime in HgCdTe Structures by Using the Method Based on Mutual Correlation Between the Concentration of Electrical Particles

We perform a theoretical study of the bulk generation-recombination mechanisms, and the carrier lifetime in n- and p-type long- and mid-wavelength infrared HgCdTe structures at liquid nitrogen (LN) temperature has been done. This article is a continuation of our previous work and presents a method for calculating the excess minority carrier lifetime considering the mutual correlation between the concentration of electrons, holes, ionized impurities, and trap states resulting from the principle of charge conservation. It has been shown that recombination involving shallow impurity states in HgCdTe structures with low intrinsic concentration has a significant impact on minority carriers’ lifetime. This applies to both p- and n-type materials. The results of calculations of the carrier lifetime determined by the interband processes: radiative, Auger 1 and 7, recombination involving impurities, as well as and Shockley–Read–Hall (SRH) mechanisms related to mercury vacancies have been compared with experimental data presented by other authors. By analyzing the published calculations made by American researchers, the values of the overlap integrals <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert {F}_{1}{F}_{2} \vert $ </tex-math></inline-formula> for Auger processes were determined, which allowed to obtain a good compliance of our calculations with the experimental values. In this article, the cross sections for SRH recombination with the participation of mercury vacancies were estimated. These values are lower than those previously presented by other researchers. By verifying the results of the calculations with the experimental data, we confirmed the effectiveness of the proposed method.

Влияние условий формирования кремниевых диодов на их обратные токи

In this work, a study was made of the influence of silicon diode manufacturing technology on the emergence of generation and recombination centers. The electrical characteristics of p-n junctions formed in different ways on n-type silicon substrates were compared: a) the p-type layer was created by the diffusion method; b) the p-type layer was formed by ion implantation into an epitaxial n-layer preliminarily grown on the substrate; c) two n- and p-type epitaxial layers were successively deposited on the substrate. It has been established that for diodes based on a double epitaxial layer, the direct and reverse current-voltage characteristics (CVC) are due to the diffusion mechanism, and the structures themselves have a low concentration of recombination centers. At the same time, in diodes based on the diffusion method and ion implantation, the CVCs are due to the generation-recombination mechanism. With reverse bias, electron-phonon processes play a significant role in the formation of the CVC, and with forward bias, carrier recombination in the region of the space charge of the p-n junction. The concentrations and energies of recombination centers have been determined.

Influence of formation conditions of silicon diodes on their reverse currents

In this work, a study was made of the influence of silicon diode manufacturing technology on the emergence of generation and recombination centers. The electrical characteristics of p-n junctions formed in different ways on n-type silicon substrates were compared: a) the p-type layer was created by the diffusion method; b) the p-type layer was formed by ion implantation into an epitaxial n-layer preliminarily grown on the substrate; c) two n- and p-type epitaxial layers were successively deposited on the substrate. It has been established that for diodes based on a double epitaxial layer, the direct and reverse current-voltage characteristics (CVC) are due to the diffusion mechanism, and the structures themselves have a low concentration of recombination centers. At the same time, in diodes based on the diffusion method and ion implantation, the CVCs are due to the generation-recombination mechanism. With reverse bias, electron-phonon processes play a significant role in the formation of the CVC, and with forward bias, carrier recombination in the region of the space charge of the p-n junction. The concentrations and energies of recombination centers have been determined. Keywords: forward and reverse current-voltage characteristic, p-n junction, diffusion, ion implantation, epitaxy, recombination centers, the Poole--Frenkel effect, electron-phonon interaction.

Detailed description of the transient effect of radiative carrier transition in the bulk of semiconductor: The case of gallium antimonide

Upon solving the differential equation related to the rate of accumulation of photo-generated carriers in the respective bands of GaSb that involves radiative generation-recombination mechanisms under constant illumination in the entire bulk of the material, the transient response (time dependence) of the photo-generated carrier density and the excess carrier lifetimes during illumination and after switching-off illumination are described for a system under different injection levels. The rates of variations of the photo-generated carrier density and the radiative excess carrier lifetimes at the initial stages of the illumination and after switching-off the illumination are evaluated at different injection levels. The injection level dependences of the effective values of the photo-generated carrier density and the radiative excess carrier lifetimes are described. The competition of the thermal and the illumination effects in the band to band radiative recombination mechanism is also described thoroughly.

Room temperature low frequency noise in n+-InAs/n-InAsSbP/InAs/p-InAsSbP double heterostructure infrared photodiodes

Low frequency forward current noise as well as the photocurrent noise are studied in InAsSbP/InAs double heterostructure (DH) photodiodes, in the frequency range 1–104 Hz. The photocurrent noise in DH photodiodes is significantly lower than in single heterostructure (SH) photodiodes. The forward current noise in a DH diode exhibiting the 1/f frequency dependence is also much lower than that in SH diodes. However, in some DH diodes, it is the generation-recombination mechanism that provides the dominant contribution to the forward current noise; in this case the noise level is significantly higher. At sufficiently high forward current densities, the noise decreases with current. The observed generation-recombination noise spectrum cannot be described within the conventional theory.

Influence of Temperature on the Output Parameters of a Photovoltaic Module Based on Amorphous Hydrogenated Silicon

The light load current-voltage characteristics of a solar photovoltaic module based on amorphous hydrogenated silicon have been studied at different temperatures under conditions of natural solar illumination (Рrad = 870 ± 10 W/m2). It has been found that the temperature dependence of the photocurrent has two slopes due to a change in the generation–recombination mechanism. The increase in the value of the short-circuit current with increasing temperature of the photovoltaic module is explained by a rise in the drift lengths of minority charge carriers due to an increase in the lifetime of minority carriers. In this case, the quasi Fermi level shifts to the conduction band, and the concentration of recombination centers decreases due to recharging of defective levels (D0 → D–). The decrease in the value of the open-circuit voltage with increasing temperature is explained by the exponential increase in the reverse saturation current and decrease in the band gap of the semiconductor. It has been found that the fill factor (FF) of the current–voltage characteristics decreases with increasing temperature, most likely due to a decrease in the shunt resistance (Rsh), which connects parallel to the p–n junction, consists of parasitic resistances, and leads to an increase in leakage currents. The temperature coefficient of the maximum output power has a positive value in the range of 320–332 K, i.e., increases with temperature. It has been revealed that the values of shunt and series resistance decrease with increasing temperature. A large loss of power output (up to 19%) has been observed on the series resistance of the solar photovoltaic module in the temperature range of 320–332 K. With increasing temperature, the loss of generated power on the shunt resistance grows sublinearly. The efficiency of the solar photovoltaic module decreases from 7.95 to 7.65% and has a coefficient of temperature dependence of efficiency, which decreases from $${{K}_{{{\text{Ef}}{{{\text{f}}}_{1}}}}}$$ ≈ –0.046 to $${{K}_{{{\text{Ef}}{{{\text{f}}}_{2}}}}}$$ ≈ –0.029%/K.

Negative and positive terahertz and infrared photoconductivity in uncooled graphene

We develop the model for the terahertz (THz) and infrared (IR) photoconductivity of graphene layers (GLs) at room temperature. The model accounts for the linear GL energy spectrum and the features of the energy relaxation and generation-recombination mechanisms inherent at room temperature, namely, the optical phonon absorption and emission and the Auger interband processes. Using the developed model, we calculate the spectral dependences of the THz and IR photoconductivity of the GLs. We show that the GL photoconductivity can change sign depending on the photon frequency, the GL doping and the dominant mechanism of the carrier momentum relaxation. We also evaluate the responsivity of the THz and IR photodetectors using the GL photoconductivity. The obtained results along with the relevant experimental data might reveal the microscopic processes in GLs, and the developed model could be used for the optimization of the GL-based photodetectors.

Analysis injection area-dark current characteristics for mid-wavelength HgCdTe photodiodes

In this paper, we study the relationship between dark current mechanism and the injection area of mid-wavelength infrared (MWIR) HgCdTe photovoltaic detectors. A simultaneous-mode nonlinear fitting program for n-on-p mid-wavelength HgCdTe infrared detectors is reported. It is found that the impact of diffusion mechanism gradually weakens and the effect of generation-recombination mechanism becomes more significant as the area of injection increasing under forward bias. The effect of trap-assisted tunneling mechanism gradually weakens as the area of injection increasing under middle reverse bias and band-to-band tunneling mechanism has less impact on dark current of MWIR HgCdTe photodiodes. And as the area of injection increasing, the effect of surface leak mechanism is gradually decrease. Finally, we find the reversed welding pressure and the arrangement of common electrode for MWIR HgCdTe Photodiodes also impacts diffusion mechanism and generation-recombination mechanism under forward bias.

Integration of an InSb photodetector on Si via heteroepitaxy for the mid-infrared wavelength region

In this study, InSb p-i-n photodetectors with In0.82Al0.18Sb barrier layers were grown on a (100) 6° offcut Si substrate by heteroepitaxy via an AlSb/GaSb buffer. Based on an interfacial misfit array growth mode, the dislocations at the GaSb/Si and InSb/AlSb interfaces accommodated the lattice mismatch. The In0.82Al0.18Sb barrier layer increased the 77 K R0A of the detector. From 180 K to 300 K, the generation-recombination mechanism dominated the dark current generation in the detector and surface leakage became dominant below 120 K. The detector exhibited a 77 K responsivity of 0.475 A/W and a Johnson-noise-limited detectivity of 3.08 × 109 cmHz1/2W-1 at 5.3 µm.

A modified and calibrated drift-diffusion-reaction model for time-domain analysis of charging phenomena in electron-beam irradiated insulators

This paper presents a modified self-consistent drift-diffusion-reaction model suitable for the analysis of electron-beam irradiated insulators at both short and long time scales. A novel boundary condition is employed that takes into account the reverse electron current and a fully dynamic trap-assisted generation-recombination mechanism is implemented. Sensitivity of the model with respect to material parameters is investigated and a calibration procedure is developed that reproduces experimental yield-energy curves for uncharged insulators. Long-time charging and yield variations are analyzed for stationary defocused and focused beams as well as moving beams dynamically scanning composite insulators.

Small-pixel long wavelength infrared focal plane arrays based on InAs/GaSb Type-II superlattice

The paper reports a 640 × 512 long wavelength infrared focal plane arrays (FPAs) with 15 × 15 μm2 pixels pitch based on the type II InAs/GaSb superlattice. Material grown on a 3 in. GaSb substrate exhibits a 50% cutoff wavelength of 10.2 μm across the entire wafer. The peak quantum efficiency of the detector reaches 28% at 9.1 μm without anti-reflecting coating. Maximal resistance-area products of 8.95 Ω·cm2 at 77 K and 24.4 Ω·cm2 at 45 K are achieved in a single element device indicating that the generation-recombination and tunneling mechanisms dominate the device dark current, respectively. The peak Johnson Detectivity reaches 9.66 × 1011 cm Hz1/2/W at 9.1 μm with the bias voltage of 80 mV. In the whole zone, the operability and non-uniformity for the responsivity are 97.74% and 6.41% respectively. The average noise equivalent temperature difference of 31.9 mK at 77 K is achieved with an integration time of 0.5 ms, a 300 K background and f/2 optics.

Temperature-dependent current–voltage characteristics and ultraviolet light detection of heterojunction diodes comprising n-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite films and p-type silicon substrates

Heterojunction diodes comprising poorly (1 at. %) nitrogen-doped n-type ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films and p-type Si substrates were prepared in nitrogen and hydrogen mixed gas atmosphere by coaxial arc plasma deposition. Dark current density–voltage (J–V) characteristics were studied in the temperature range of 200–400 K, in order to investigate the current transport mechanism through the fabricated heterojunctions. The temperature dependence of the ideality factor and reverse saturation current reveals that carrier transport predominantly occurs in the generation–recombination mechanism and, at low temperatures, it accompanies tunneling via weak traps. The heterojunctions surely exhibited photodetection for 254 nm ultraviolet light illumination. It is expected that photocarriers will be generated at UNCD grains and transported through an a-C:H matrix.

SiC polytypes and doping nature effects on electrical properties of ZnO-SiC Schottky diodes

Electrical properties of ZnO/SiC Schottky diodes with two SiC polytypes and N and P doping are investigated. Characterization was performed through I–V and C–V–f measurements. Schottky barrier height (Φb), ideality factor (n), and series resistance (Rs) were extracted from forward I–V characteristics. (Φb), carrier's concentrations (Nd-Na) and (Rs) frequency dependence were extracted from C–V–f characteristics. The extracted n values suggest that current transport is dominated by interface generation-recombination and/or barrier tunneling mechanisms. When changing SiC polytypes, the rectifying ratio of ZnO/n-4HSiC is found to be twice that of ZnO/n-6HSiC. A change in doping nature gave a leakage current ratio of 40 between ZnO/p-4HSiC and ZnO/n-4HSiC. These results indicate that ZnO/p-4HSiC diodes have a complex current transport compared to diodes on n-type SiC. From I-V measurements, barrier height values are 0.63eV, 0.65eV and 0.71eV for heterojunction grown on n-6HSiC, n-4HSiC and p-4HSiC, respectively. C-V measurements gave higher values indicating the importance of interface density of states. Nss values at 1MHz frequency are 4.54×1011eV−1cm−2, 3×1012eV−1cm−2 and 8.13×1010eV−1cm−2 for ZnO/n-6HSiC, ZnO/n-4HSiC and ZnO/p-4HSiC, respectively. Results indicate the importance of SiC polytypes and its doping nature.

Temperature Dependence Study of Mesa-Type InGaAs/InAlAs Avalanche Photodiode Characteristics

Avalanche photodiodes (APDs) are key optical receivers due to their performance advantages of high speed, high sensitivity, and low noise. The most critical device parameters of APD include the avalanche breakdown voltage and dark current. In this work, we study the temperature dependence of the breakdown voltage and dark current of the mesa-type APD over a wide temperature range of 20–145°C. We institute an empirical model based on impact ionization processes to account for the experimental data. It is shown that highly stable breakdown characteristics of mesa-type APD can be attained with the optimization of the multiplication layer design. We have achieved excellent stability of avalanche breakdown voltage with a temperature coefficient of 0.017 V/°C. The temperature dependence of dark current is attributed to generation-recombination mechanism. The bandgap energy is estimated to be about 0.71 eV based on the temperature variation of dark current, in good agreement with the value for InGaAs.

Theoretical utmost performance of (100) mid-wave HgCdTe photodetectors

HgCdTe detectors designed to detect mid-wavelength (3–5 μm) infrared radiation must be cooled to reach the required performance. The cooling requirement makes the sensor system both expensive and bulky and the fundamental goal is to reach higher operating temperature condition preserving near background limited performance with high detectivity and high speed response at the same time. In order to reach higher operating temperature condition the thermal generation rate must to be suppressed under the photon generation rate. Except Auger 7 generation-recombination process, p-type HgCdTe is mostly limited by technology dependent Shockley-Read-Hall generation-recombination mechanism. One of the ways to reduce the trap density is a growth of the (100) HgCdTe on GaAs substrates. That orientation allows reaching lower carrier concentration ~5 × 1014 cm−3 in comparison to the commonly used (111) orientation ~5 × 1015 cm−3 in mid-wavelength infrared range. In addition, it was presented that Shockley-Read-Hall traps density could be reduced to the level of ~4.4 × 108 cm−3. The theoretical simulations related to the utmost performance of the (100) HgCdTe Auger suppressed structures are presented. Dark current is reported to be reduced by more than one order of magnitude within the range ~6 × 10−2–3 × 10−3 A/cm2. Detectivity increases within range ~3–12 × 1011 cm Hz1/2/W (wavelength ~5 μm) at temperature 200 K and voltage 200 mV.

Low-Frequency Noise in Advanced SiGe:C HBTs—Part II: Correlation and Modeling

In part I, we extensively analyzed the results of the low-frequency noise characterization in advanced SiGe:C heterojunction bipolar transistors. In this paper, we demonstrate that base and collector noise spectral densities are partially correlated. The correlation is investigated by studying the coherence function at different bias conditions. The coherence reveals a frequency dependence at lower bias due to the presence of dominant generation–recombination mechanisms, whereas at higher bias, the coherence approaches unity. The bias dependence of the coherence is studied in several transistor geometries. In addition, a partially correlated base and collector 1/f noise model is proposed and implemented in HiCuM. Modeling results are in agreement with the measured data.

Growth and characterization of metamorphic InAs/GaSb tunnel heterojunction on GaAs by molecular beam epitaxy

The structural, morphological, optical, and electrical transport characteristics of a metamorphic, broken-gap InAs/GaSb p-i-n tunnel diode structure, grown by molecular beam epitaxy on GaAs, were demonstrated. Precise shutter sequences were implemented for the strain-balanced InAs/GaSb active layer growth on GaAs, as corroborated by high-resolution X-ray analysis. Cross-sectional transmission electron microscopy and detailed micrograph analysis demonstrated strain relaxation primarily via the formation of 90° Lomer misfit dislocations (MDs) exhibiting a 5.6 nm spacing and intermittent 60° MDs at the GaSb/GaAs heterointerface, which was further supported by a minimal lattice tilt of 180 arc sec observed during X-ray analysis. Selective area diffraction and Fast Fourier Transform patterns confirmed the full relaxation of the GaSb buffer layer and quasi-ideal, strain-balanced InAs/GaSb heteroepitaxy. Temperature-dependent photoluminescence measurements demonstrated the optical band gap of the GaSb layer. Strong optical signal at room temperature from this structure supports a high-quality material synthesis. Current–voltage characteristics of fabricated InAs/GaSb p-i-n tunnel diodes measured at 77 K and 290 K demonstrated two bias-dependent transport mechanisms. The Shockley–Read–Hall generation–recombination mechanism at low bias and band-to-band tunneling transport at high bias confirmed the p-i-n tunnel diode operation. This elucidated the importance of defect control in metamorphic InAs/GaSb tunnel diodes for the implementation of low-voltage and high-performance tunnel field effect transistor applications.

Device behavior of an In/p-Ag(Ga,In)Te2/n-Si/Ag heterojunction diode

In this work, p-(Ag–Ga–In–Te) polycrystalline thin films were deposited on soda-lime glass and n-type Si substrates by e-beam evaporation of AgGa0.5In0.5Te2 crystalline powder and the thermal evaporation of Ag powder, sequentially in the same chamber. The carrier concentration and mobility of the Ag–Ga–In–Te (AGIT) film were determined as 5.82×1015cm−3 and 13.81cm2/(Vs) as a result of Hall Effect measurement. The optical analysis indicated that the band gap values of the samples were around 1.58eV. The structural analysis was carried out by means of X-ray diffraction. Current–Voltage (I–V) measurements depending on the sample temperature were performed to investigate the device characteristics and the dominant conduction mechanism in an In/p-AGIT/n-Si/Ag structure. The series and shunt resistances were calculated by the help of parasitic resistance analysis as 5.73 and 1.57×104Ωcm2, respectively at room temperature. The ideality factors and barrier heights were evaluated as a function of sample temperature. In the low bias region, the thermionic emission together with the generation–recombination mechanism was investigated as the dominant transport mechanism; however, in the high bias region, space charge limited current was analyzed as the other effective mechanism in the carrier conduction. The built-in potential of the device was also determined by the help of capacitance–voltage measurements.

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

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