Light coupling characteristics of corrugated quantum-well infrared photodetectors

Corrugated quantum-well infrared photodetectors (C-QWIPs) offer simple detector architectures for large-format infrared focal plane arrays (FPAs). The detector relies on inclined sidewalls to couple normal incident light into the absorbing material. Based on a simplified geometrical-optics (GO) model, this light coupling scheme is expected to be effective with little wavelength dependence. In this work, we apply the modal transmission-line (MTL) modeling technique to study in detail its light coupling characteristics and compare the results with the GO model and experimental data. We find that the results of the GO model agree reasonably well with those of the rigorous MTL model for corrugations with metal cover, and both modeling procedures are consistent with experimental data. In particular, both models predict similar increase in the quantum efficiency /spl eta/ with the size of the corrugations, and both indicate similar limiting /spl eta/ when the corrugation becomes very large. For linear corrugations with thick substrates, the maximum /spl eta/ is about 30%. On the other hand, there are also significant differences between the two models when the effects of phase coherence are important. Since the phase of the radiation is taken into account in the MTL formalism but not in the GO formalism, the MTL model is more generally applicable and is more capable of explaining different detector characteristics. For example, it predicts a smaller /spl eta/ for air or epoxy-covered C-QWIPs because of finite optical transmission through the sharp corners in the corrugations, and it indicates an oscillatory function of /spl eta/ because of the existence of optical fringes. It also reveals the wavelength dependence of the coupling, which becomes more pronounced as the thickness of the substrate layer is reduced.     

Refined model for the current-voltage characteristics of quantum-well infrared photodetectors

The temperature dependences of the dark current of quantum-well infrared photodetectors are investigated experimentally. It is established that the pre-exponential factor in the analytical expression for the photodetector current-voltage characteristics varies linearly with temperature. On the basis of the results obtained, it is suggested that the temperature dependence of the photodetector??s dark current is determined by the thermal excitation of charge carriers to a band characterized by a two-dimensional density of states. In the context of this suggestion, a refined model for the current-voltage characteristics is proposed. The model takes into account the thermal generation of charge carriers in a band with a two-dimensional density of states and the electric field dependence of the thermal activation energy for the quantum-well ground state and of the drift velocity of the carriers in the barrier conduction band.     

Low frequency noise spectroscopy in InAs/GaAs resonant tunneling quantum dot infrared photodetectors

We have studied the temperature dependence of low-frequency noise in InAs–GaAs resonant tunneling quantum dot infrared photodetectors (T-QDIPs). The noise in these devices has been investigated in the temperature range of 78–300 K. The noise spectrum showed a weak Lorentzian component superimposed upon the 1/f^γ spectrum. The change in the cut-off frequency of the Lorentzian was analyzed as a function of temperature. The activation energy of the trap associated with this Lorentzian was obtained as 0.155 eV, which is in good agreement with the energy of the lowest energy state in the quantum dot.     

Carrier scattering approach to the origins of dark current in mid and far-infrared (terahertz) quantum-well intersubband photodetectors(QWLPs)

A carrier scattering approach is taken in an analysis of the affect on the dark current of extending the operating wavelength of conventional bound to continuum quantum-well intersubband photodetectors. It is found that both the sequential tunneling and the thermionic emission contributions to the dark current increase as the wavelength of the detector is extended from the mid- to far-infrared. Dark current designs rules are derived     

High responsivity InP-InGaAs quantum-well infrared photodetectors: characteristics and focal plane array performance

We report the detailed characteristics of long-wavelength infrared InP-In/sub 0.53/Ga/sub 0.47/As quantum-well infrared photodetectors (QWIPs) and 640/spl times/512 focal plane array (FPA) grown by molecular beam epitaxy. For reliable assessment of the detector performance, characterization was performed on test detectors of the same size and structure with the FPA pixels. Al/sub 0.27/Ga/sub 0.73/As-GaAs QWIPs with similar spectral response (/spl lambda//sub p/=/spl sim/7.8 /spl mu/m) were also fabricated and characterized for comparison. InP-InGaAs QWIPs (20-period) yielded quantum efficiency-gain product as high as 0.46 under -3-V bias with a 77-K peak detectivity above 1/spl times/10/sup 10/ cm/spl middot/Hz/sup 1/2//W. At 70 K, the detector performance is background limited with f/2 aperture up to /spl sim/ 3-V bias where the peak responsivity (2.9 A/W) is an order of magnitude higher than that of the AlGaAs-GaAs QWIP. The results show that impact ionization in similar InP-InGaAs QWIPs does not start until the average electric-field reaches /spl sim/25 kV/cm, and the detectivity remains high under moderately large bias, which yields high responsivity due to large photoconductive gain. The InP-InGaAs QWIP FPA offers reasonably low noise equivalent temperature difference (NETD) even with very short integration times (/spl tau/).70 K NETD values of the FPA with f/1.5 optics are 36 and 64 mK under bias voltages of -0.5 V (/spl tau/=11 ms) and -2 V (/spl tau/=650 /spl mu/s), respectively. The results clearly show the potential of InP-InGaAs QWIPs for thermal imaging applications requiring high responsivity and short integration times.     

Comparison of hole and electron intersubband absorption strengthsfor quantum well infrared photodetectors

It is well known that the hole intersubband absorption of normally incident (TE polarized) radiation is nonzero for p-doped quantum well infrared photodetectors (p-QWIP's) which have been fabricated without an optical grating. This present paper shows from k&oarr;·p&oarr; theory that, for typical p-QWIP designs, this hole intersubband absorption of TE polarized radiation (without the help of an optical grating) is significantly smaller than the electron intersubband absorption of TE polarized radiation in those n-doped QWIP's (n-QWIP's) fabricated with an optical grating. A second result of this present work is that, even when there is significant mixing of the light and heavy hole states, the p-QWIP absorption of TE polarized radiation (without the help of an optical grating) is still much smaller than the n-QWIP absorption of TE polarized radiation (with the help of an optical grating). The reason is that the mixing of light and heavy hole states never increases the amount of |S〉-symmetry in the mixed hole wave function beyond the amount of |S〉-symmetry which was present in the unmixed, purely light hole state. Finally, this present paper shows from k&oarr;·p&oarr; theory that strained layer growth on an (001) substrate does not significantly affect the strength of the hole intersubband absorption. The reason is that the Hamiltonian describing uniaxially strained quantum wells has precisely the same (tetragonal) symmetry as the Hamiltonian describing carrier confinement in unstrained quantum wells. All of these results are important in choosing a QWIP device design     

Design and characterization of a CMOS preamplifier for quantum well infrared photodetectors

A preamplifier based on the source-follower direct injection (SFDI) topology for use in read-out integrated circuits (ROIC) of quantum-well infrared photodetectors focal plane arrays (QWIP-FPA) is demonstrated. The fabricated circuit shows high linearity, high integration time (from hundreds of μs to few ms) and low current detection capabilities for a wide range of input current (order of few pA). This performance was achieved through the use of a Poly1-Poly2 capacitor that, although presenting some penalties in area consumption, provides a higher linearity, lower leakage current and higher temperature stability than all others capacitors found in literature. Secondary effects such as charge injection and clock feed-through are observed in the experimental results and classical techniques, like the use of DUMMY transistor, are shown to be effective in minimizing these effects and maximizing the linearity of the response. The overall results indicate that this circuit architecture has a great potential to be practically integrated in larger QWIP-FPA ROICs, showing an improved performance relating to previous works in literature.     

改进器件工艺降低硅光电探测器暗电流

为降低硅光电探测器ＰＮ结反向暗电流，可在器件制作工艺中采用一系列完美晶体器件工艺（ＰＣＤＴ）。在实验过程中，对吸除工艺，应力补偿工艺等作了改进，进一步降低了反向暗电流。     

Low dark current and internal gain mechanism of GaN MSM photodetectors fabricated on bulk GaN substrate

Metal-semiconductor-metal ultraviolet photodetectors are fabricated on low-defect-density homoepitaxial GaN layer on bulk GaN substrate. The dislocation density of the homoepitaxial layer characterized by cathodoluminescence mapping technique is ∼5 × 10⁶ cm⁻². The photodetector with a high UV-to-visible rejection ratio of up to 1 × 10⁵ exhibits a low dark current of <2 pA at room temperature under 10 V bias. The photo-responsivity of the photodetector gradually increases as a function of applied bias, resulting in a photodetector quantum efficiency exceeding 100% at above medium bias. The photo-responsivity also shows a dependence on the incident optical power density and illumination conditions. The internal gain mechanism of the photodetector is attributed to photo-generated holes trapped at the semiconductor/metal interface as well as high-field-induced image-force lowering effect.     

Reduction of dark current in AlGaN-GaN Schottky-barrier photodetectors with a low-temperature-grown GaN cap layer

AlGaN-GaN-based UV Schottky-barrier photodetectors with (i.e., sample A) and without (i.e., sample B) the low-temperature (LT) GaN cap layer were both fabricated. It was found that we could achieve a lower leakage current from sample A. Under reverse bias, it was found that sample A showed a dark current as low as 2/spl times/10/sup -11/ A at -5 V. In contrast, the dark current of sample B was at least one order of magnitude larger. With an incident light wavelength of 320 nm and a -1 V reverse bias, the measured responsivity was around 0.03 and 0.015 A/W for samples A and B, respectively.     

Growth and characterization of InGaAs/InP p-quantum-well infrared photodetectors with extremely thin quantum wells

High-quality InGaAs/InP quantum wells with ultra-narrow well widths (∼10?) and peak response at 4.55 μm were grown by gas source molecular beam epitaxy. These structures were characterized by cross-sectional tunneling microscopy (XSTM), double-crystal x-ray diffraction (DCXRD), and cross-sectional transmission electron microscopy (XTEM). Based on the structural parameters determined by XTEM, XSTM, and DCXRD, the field dependent photocurrent spectra were simulated using a six-band effective bond-orbital model. The theoretical calculations are in excellent agreement with experimental data. When used to fabricate p-type InGaAs/InP quantum-well infrared photodetectors (QWIPs), and combined with the high responsivity of 8.93 μm n-type InGaAs/InP QWIPs, these structures offer the possibility of dual band monolithically integrated QWIPs.     

Improvement of dark current using InP/InGaAsP transition layer in large-area InGaAs MSM photodetectors

A large-area InGaAs metal-semiconductor-metal (MSM) photodetector with 1/spl times/1 mm/sup 2/ photoactive area for free-space optical communication applications has been designed, fabricated, and characterized. Interdigitated electrodes of 2-/spl mu/m widths and 15-/spl mu/m spacings are designed to maximize the responsivity, and enable MSM photodetectors to reach a maximum responsivity at 1.53-/spl mu/m wavelength. By employing a two-step InP/InGaAsP transition layer, the dark current density of 45 fA//spl mu/m/sup 2/ was achieved at 10-V bias and at room temperature. Dark current-bias voltage curves were measured as a function of temperature from 40 to 270 K to estimate the activation energy. A 3-dB bandwidth of 210 MHz was obtained at a 10-V bias, and the measured result was compared with the designed bandwidth.     

Optical heterodyne detection and microwave rectification up to 26GHz using quantum well infrared photodetectors

We have demonstrated heterodyne detection up to an intermediate frequency of 26.5 GHz using quantum well infrared photodetectors. A CO ₂ laser and a lead-salt tunable diode laser were used as the infrared sources. Heterodyne detection experiments measure the high frequency behavior of photoexcited electrons and their transport properties. We have also carried out microwave rectification experiments which measure the high frequency behavior associated with the dark-current electron-transport processes     

Current voltage modeling of current limiting mechanisms in HgCdTe focal plane array photodetectors

An automated iterative nonlinear fitting program has been developed to model current-voltage (I–V) data measured on HgCdTe infrared (IR) detector diodes. This model includes the ideal diode diffusion, generation-recombination, band-to-band tunneling, trap-assisted tunneling (TAT), and avalanche breakdown as potential current limiting mechanisms in an IR detector diode. The modeling presented herein allows one to easily distinguish, and more importantly to quantitatively compare, the amount of influence each current limiting mechanism has on various detectors’ I–V characteristics. Longer cutoff wavelength detectors often exhibit significant current limitations due to tunneling processes. The temperature dependence of these tunneling characteristics is thoroughly investigated for two diodes.     

High temperature operation of long-wavelength infrared superlattice detector with supressed dark current

Superlattice (SL) photodetectors operating with a cutoff wavelength of lambda = 10 mum are demonstrated to respond up to a temperature of T = 140 K with a nonunity gain enabling a high responsivity of Rfr = 25 A/W. The improvement in detector performance is achieved by the optimisation of SL heterodiode design in which suppression of dark current is realised without significant impact on the photocurrent.     

Influence of two-dimensional magnetic photonic quantum wells on resonant tunneling spectral character

The non-magnetic material closed photonic quantum well (PQW) and magnetic material PQW structures based on the non-magnetic material open PQW are proposed. The transmission spectra and the field distributions of these three PQW structures are calculated by finite-difference time-domain method, the quantized energy states are researched, and the feasibility of enhancing spectral intensity significantly by selfstructure is disclosed. It is found that the optical transmittance of the magnetic PQW is close to 1, and the energy loss is less compared to non-magnetic PQW.Compared with the closed PQW structures, the device's volume can be reduced, the degree of free regulation of the energy band project can be increased, and more photon bound states can be obtained. The results show that the open PQW is the traveling wave well, and its capability of capturing photons is weak. However, the closed PQW and the magnetic PQW are standing wavewells. Their capabilities for capturing photons are strong,while the light field gradient of the material PQW is bigger.     

Growth and characterization of n-type InP/InGaAs quantum well infrared photodetectors for response at 8.93 µm

We present experimental results on the growth and characterization of n-type InGaAs/InP quantum-well intersubband photodetectors for use at 8.93 μm. High-quality InGaAs/InP multiple quantum wells were grown by gas source molecular beam expitaxy, and then characterized by double-crystal x-ray diffraction and cross-sectional transmission electron microscopy. Based upon the structural parameters determined by these methods, the photocurrent response spectra were simulated using a six-band effective bond-orbital model. The theoretical results are in excellent agreement with experimental data. Additional important device characteristics such as dark current, spectral response, and absolute responsivity are also presented.     

Unambiguous determination of quantum capture, carrier diffusion,and intrinsic effects in quantum-well laser dynamics usingwavelength-selective optical modulation

A novel wavelength-dependent optical modulation technique capable of explicitly delineating the effects of quantum capture, carrier diffusion, and other intrinsic effects in quantum-well laser dynamics is described. Results for a compressively strained multiple-quantum-well laser are presented     

The effect of compressive strain on the performance of p-typequantum-well infrared photodetectors

A detailed study of the performance of compressively strained p-type III-V quantum-well infrared photodetectors (p-QWIPs) is presented in this work. Three device structures composed of InGaAs-GaAs, InGaAs-AlGaAs, and InGaAs-AlGaAs-GaAs for normal incidence absorption have been fabricated and analyzed, with the results being compared with similar reported unstrained p-QWIPs. In all three QWIP structures, the quantum-well layers are under biaxial compressive strain ranging from -0.8% to -2.8%, while the barrier layers are lattice-matched to the substrate. The detection peaks of the quantum-well infrared photodetectors ranged from 7.4 to 10.4 μm. The detectors utilized the bound-to-continuum, bound-to-quasi-bound, and step bound-to-miniband intersubband transitions for infrared detection. The results showed that responsivities of up to 90 mA/W and detectivities from 10⁹ to over 10¹⁰ cm√Hz/W are achieved under moderate applied bias and at reasonable operating temperatures (from 60 to 80 K), demonstrating the viability of the strained-layer p-doped quantum-well infrared photodetectors for staring focal plane array applications     

Dependence of the electron capture velocity on the quantum-well depth in semiconductor lasers

Three laser structures with a single strained InGaAs quantum well of different depths and a GaAs or Al_0.1Ga_0.9As waveguide region are grown by metal-organic chemical vapor deposition. Using the experimentally determined values of the threshold current density and internal differential quantum efficiency, the velocity of electron capture into the quantum well is calculated for each of these structures. It is found that the capture velocity into deep quantum wells is significantly lower than into shallow ones.