Room temperature quantum cascade detector operating at 4.3 μm

A strain-compensated InP-based InGaAs/InAlAs quantum cascade detector grown by solid source molecular beam epitaxy is demonstrated. The device operates at 4.3 μm up to room temperature (300 K) with a responsivity of 1.27 mA/W and a Johnson noise limited detectivity of 1.02×10⁷ cm·Hz^1/2/W. At 80 K, the responsivity and detectivity are 14.55 mA/W and 1.26×10¹⁰ cm·Hz^1/2/W, respectively. According to the response range, this detector is much suitable for greenhouse gas detection.     

Uncooled InAs-GaSb type-II infrared detectors grown on GaAssubstrates for the 8-12-μm atmospheric window

We report on the growth and characterization of type-II infrared detectors with an InAs-GaSb superlattice active layer for the 8-12-μm atmospheric window at 300 K. The material was grown by molecular beam epitaxy on semi-insulating GaAs substrates. Photoconductive detectors fabricated from the superlattices showed 80% cutoff at about 12 μm at room temperature. The responsivity of the device is about 2 mA/W with a 1-V bias (E=5 V/cm) and the maximum measured detectivity of the device is 1.3×10⁸ cm.Hz^1/2/W at 11 μm at room temperature. The detector shows very weak temperature sensitivity. Also, the extracted effective carrier lifetime, τ=26 ns, is an order of magnitude longer than the carrier lifetime in HgCdTe with similar bandgap and carrier concentration     

Room temperature unpassivated InAs p-i-n photodetectors grown bymolecular beam epitaxy

An unpassivated InAs p-i-n photodetector with excellent performance at room temperature was demonstrated. The zero-bias resistance area products of the diode with 720-nm thick i-layer are 8.1 Ω-cm² at room temperature and as high as 1.3 M Ω-cm² at 77 K. At 77 K, the diode exhibits a breakdown voltage exceeding 13 V. When tested under a 500 K blackbody source, the measured detectivity limited by Johnson noise is 1.2×10¹⁰ cm-Hz^½/W at room temperature and 8.1×10 ¹¹ cm-Hz^½/W at 77 K. To our knowledge, this is the best data for a room temperature infrared detector     

液氮制冷的AlGaN/GaN HEMT太赫兹探测器阵列特性研究

为充分发挥AlGaN/GaN高电子迁移率晶体管 (High-Electron-Mobility Transistor, HEMT)太赫兹探测器阵列的高电子迁移率优势,文中研究了HEMT太赫兹探测器阵列在77 K下的探测特性。使用液氮杜瓦为降温主体搭建了适用于焦平面 (Focal-Plane Array, FPA)芯片的低温系统,实现了对焦平面芯片常温与低温下的对比测试。温度从300 K降到77 K时,探测器阵列像元的平均响应度提高近3倍,平均噪声有小幅增大,340 GHz时平均噪声等效功率 (Noise Equivalent Power, NEP)从45.1 pW/Hz1/2降低到了19.4 pW/Hz1/2,灵敏度提高两倍以上。与硅透镜耦合的单元探测器相比,阵列像元的灵敏度提升仍有较大空间。主要是由于各像素点最佳工作电压的不一致,导致在给定统一工作电压下像元间的响应度和噪声都表现出较大的离散性,文中讨论了降低最佳工作电压离散度的可能解决方案。     

CO2pulsed laser radiation tellurium detectors

Subnanosecond detectors and beam monitors for pulsed CO2laser radiation using the photon drag and optical rectification effects in tellurium are presented. Tellurium devices at 10.6 μ have a response of the order of 80 μV/kW . cm^-2with an NEP of8 times 10^{-4}W . Hz^1/2andD*of 500 cm . Hz^1/2/W which is superior to commercially available photon drag detectors and monitors. It is also expected and experimentally demonstrated that the responsivities of large area monitors can be multiplied by cutting the original area into multi-element strips and electrically connecting them in series.     

High-operating-temperature MWIR photodetector based on a InAs/GaSb superlattice grown by MOCVD

We demonstrate a high-operating-temperature(HOT)mid-wavelength InAs/GaSb superlattice heterojunction in-frared photodetector grown by metal-organic chemical vapor deposition.High crystalline quality and the near-zero lattice mis-match of a InAs/GaSb superlattice on an InAs substrate were evidenced by high-resolution X-ray diffraction.At a bias voltage of-0.1 V and an operating temperature of 200 K,the device exhibited a 50%cutoff wavelength of~4.9μm,a dark current dens-ity of 0.012 A/cm²,and a peak specific detectivity of 2.3×10⁹ cm·Hz^1/2/W.     

HEMT太赫兹探测器响应度和NEP的检测与分析

在0.8～1.1 THz内,对AlGaN/GaN高电子迁移率晶体管(HEMT)太赫兹探测器的响应度和噪声等效功率进行了具体测试和分析。在太赫兹波辐射下,HEMT太赫兹探测器源漏端产生能被栅压灵敏调控的直流光电流。该型探测器在300 K和77 K下的电流响应度分别为83 mA/W和4.1 A/W,电压响应度分别为4 kV/W和50 kV/W,噪声等效功率分别达到22 pW/Hz0.5和1 pW/Hz0.5。采用两种较为典型的测量方法,通过对实验结果的比较,确定了影响该类型探测器的响应度和噪声等效功率的主要因素,并提出了增强响应度和降低噪声等效功率的具体措施。     

A 850-GHz waveguide receiver employing a niobium SIS junctionfabricated on a 1-μm Si3N4 membrane

We report on a 850-GHz superconducting-insulator-superconducting (SIS) heterodyne receiver employing an RF-tuned niobium tunnel junction with a current density of 14 kA/cm², fabricated on a 1-μm Si₃N₄ supporting membrane. Since the mixer is designed to be operated well above the superconducting gap frequency of niobium (2Δ/h≈690 GHz), special care has been taken to minimize niobium transmission-line losses. Both Fourier transform spectrometer (FTS) measurements of the direct detection performance and calculations of the IF output noise with the mixer operating in heterodyne mode, indicate an absorption loss in the niobium film of about 6.8 dB at 822 GHz. These results are in reasonably good agreement with the loss predicted by the Mattis-Bardeen theory in the extreme anomalous limit. From 800 to 830 GHz, we report uncorrected receiver noise temperatures of 518 or 514 K when we use Callen and Welton's law to calculate the input load temperatures. Over the same frequency range, the mixer has a 4-dB conversion loss and 265 K±10 K noise temperature. At 890 GHz, the sensitivity of the receiver has degraded to 900 K, which is primarily the result of increased niobium film loss in the RF matching network. When the mixer was cooled from 4.2 to 1.9 K, the receiver noise temperature improved about 20% 409-K double sideband (DSB). Approximately half of the receiver noise temperature improvement can be attributed to a lower mixer conversion loss, while the remainder is due to a reduction in the niobium film absorption loss. At 982 GHz, we measured a receiver noise temperature of 1916 K     

1/f noise and specific detectivity of HgCdTe photodiodes passivatedwith ZnS-CdS films

1/f noise in HgCdTe photodiodes has been measured as a function of temperature, diode bias, and dark current. The dependence of 1/f noise on dark current was measured over a wide temperature range. At low temperatures, where surface generation and leakage current were predominant, a linear relationship between 1/f noise and dark current was observed. At higher temperatures, where diffusion current is predominant, the correlation no longer holds. The temperature dependence of 1/f noise was also determined. The temperature dependence of the 1/f noise was found to be the same as that for the surface generation and leakage currents. All the data obtained in these experiments could be fit with theoretical predictions by a simple relationship between 1/f noise and dark current. The 1/f noise in the HgCdTe photodiode varies with diode bias, temperature, and dark current only through the dependence of the surface current on these devices. The maximum specific detectivity (D*) value and the maximum signal-to noise ratio are approximately 3.51×10¹⁰ cm·Hz^1/2/W and 5096 at 50 mV reverse bias, respectively     

Room-Temperature p-n-p AlGaAsSb–InGaAsSb Heterojunction Phototransistors With Cutoff Wavelength at 2.5 $mu$ m

Novel p-n-p AlGaAsSb-InGaAsSb heterojunction phototransistors (HPTs) grown by solid-source molecular beam epitaxy have been proposed and demonstrated. The p-n-p phototransistor structure provides a higher emitter injection ratio than its n-p-n counterpart, due to the large conduction band offset and almost continuous valence band edges between InGaAsSb and AlGaAsSb quaternary alloys. The resulting HPT devices exhibit high responsivities under a bias voltage above 0.3 V. A high room-temperature spectral responsivity of 2984 A/W is achieved at 2.24 mum, corresponding to an optical gain of 1652. The 50% cutoff wavelength of spectral photoresponse at room temperature is 2.50 mum. A room-temperature specific detectivity (D^*) of 8.3times10 ¹¹ cm middot Hz^1/2/W is obtained     

Low-noise back-illuminated AlxGa1-xN-basedp-i-n solar-blind ultraviolet photodetectors

We report the growth, fabrication and characterization of Al_0.4Ga_0.6N-Al_0.6Ga_0.4N back-illuminated, solar-blind p-i-n photodiodes. The peak responsivity of the photodiodes is 27 and 79 mA/W at λ≈280 nm for bias voltages of 0 V and -60 V, respectively, with a UV-to-visible rejection ratio of more than three decades (at 400 nm). These devices exhibit very low dark current densities (~5 nA/cm² at -10 V). At low frequencies, the noise exhibits a 1/f-type behavior. The noise power density is S₀≈5×10^-25 A²/Hz at -12.7 V and the detectivity (D*) at 0 V is estimated to be in the range of 4×10¹¹-5×10¹³ cm·Hz^1/2 /W. Time-domain pulse response measurements in a front-illumination configuration indicate that the devices are RC-time limited and show a strong spatial dependence with respect to the position of the incident excitation, which is mainly due to the high resistivity of the p-type Al_0.4Ga_0.6 N layer     

Effect of laser phase noise in Sagnac interferometers

A theoretical analysis of the responsivity and the noise caused by backscattering in a Sagnac interferometer used as a sensor for reciprocal measurands, such as acoustic waves, is presented. Both Rayleigh backscattering and reflections from splices are taken into account. The noise power is found to increase proportionally to the source coherence time, and a noise equivalent phase shift in the range of 0.1×10^-6 rad r.m.s./Hz^1/2 is predicted for typical fibers and diode lasers. Experimentally, a noise equivalent phase shift of 2.5×10^-7 rad r.m.s./Hz^1/2 at 10 kHz was observed, with a detector current of 3 μA     

Uncooled thermopile infrared detector linear arrays withdetectivity greater than 109 cmHz1/2/W

We have fabricated 63-element linear arrays of micromachined thermopile infrared detectors on silicon substrates. Each detector consists of a suspended silicon nitride membrane with 11 thermocouples of sputtered Bi-Te and Bi-Sb-Te films. At room temperature and under vacuum these detectors exhibit response times of 99 ms, zero frequency D* values of 1.4× 10⁹ cmHz^1/2/W and responsivity values of 1100 V/W when viewing a 1000 K blackbody source. The only measured source of noise above 20 mHz is Johnson noise from the detector resistance. These results represent the best performance reported to date for an array of thermopile detectors. A test procedure is described that measures many of the relevant electrical, optical, and thermal properties of the detectors without specialized test structures     

A low noise 230 GHz heterodyne receiver employing 0.25-μm2 area Nb-AlOx-Nb tunnel junctions

The authors report recent results for a full-height rectangular waveguide mixer with an integrated IF matching network. Two 0.25 μm ² Nb-AlO_x-Nb superconducting-insulating-superconducting (SIS) tunnel junctions with a current density of ≈8500 A/cm² and ωRC of ≈2.5 at 230 GHz have been tested. One of these quasiparticle tunnel junctions is currently being used at the Caltech Submillimeter Observatory in Hawaii. Detailed measurement of the receiver noise have been made from 200-290 GHz for both junctions at 4.2 K. The lowest receiver noise temperatures were recorded at 239 GHz, measuring 48 K DSB at 4.2 K and 40 K DSB at 2.1 K. The 230-GHz receiver incorporates a one-octave-wide integrated low-pass filter and matching network which transforms the pumped IF junction impedance to 50 Ω over a wide range of impedances     

1-2 micron (Hg, Cd)Te photodetectors

The performance of mercury cadmium telluride detectors in the 1-2 micron spectral region has been predicted from basic material parameters. Photovoltaic devices should be characterized by specific responsivities of 1 A/W for a 1000 ohm load when transit time limited to less than 20 ns. Photoconductive detectors made from n-type material should have radiative lifetimes of 1 ms. The feasibility of high performance 1-2 micron (Hg, Cd)Te detectors has been demonstrated experimentally. Deep junction devices operating at room temperature without bias have been fabricated by impurity indiffusion. Detectivities at 1.75 microns approached 10¹⁰cm.Hz^1/2/W with open-circuit responsivities of approximately 500 V/W. In addition, 1.5 micron detectors have been fabricated from p-type, 25 Ω.cm material. With no bias at room temperature, these detectors showed D* λ>10¹⁰cm.Hz/12/W, open-circuit responsivities in excess of 10³V/W, and response times on the order of microseconds. These preliminary results indicate that detectors fabricated from the pseudobinary alloy of (Hg, Cd)Te are well suited for high speed, near infrared photodetection in which room temperature operation is required.     

Noise effects in bipolar junction transistors at cryogenic temperatures: Part I

Part I of this investigation involves theoretical and experimental characterization of the noise performance of modern silicon planar bipolar junction transistors (BJT's) above the 1/f noise frequency region in a temperature range of 60-300 K and for several difference bias conditions. At temperatures below approximately 110 K, an excess noise source as measured by the equivalent noise resistance RN, referred to the input of the device, common-base configuration, is revealed. This excess source, resulting from a generation-recombination process within the base region of the device, is shown to have a linear dependence on the base current and base resistance as KIB²rb'b², and an exponential dependence on temperature.     

Highly sensitive In0.53Ga0.47As/InP Hallsensors grown by MOVPE

High performance InP/InGaAs Hall sensors appropriate for applications requiring high sensitivity at low power dissipation, good linearity, low temperature sensitivity, and high resolution are reported. The layer structures grown by MOVPE combine a high mobility In _0.53Ga_0.47As channel with isolation by semi-insulating InP. With this design bias current related sensitivities up to 760 V/AT at sheet resistances below 840 Ω/square have been achieved, allowing high output signals at low power dissipation. Due to the active layer isolation by semi-insulating InP, bias currents are not limited by channel pinch-off or junction breakdown. This leads to absolute sensitivities as high as 12.5 V/T. Linearity errors are lower than -0.8% up to magnetic fields of 0.5 T. Temperature coefficients of the sensitivity were measured for different donor concentrations of the active layer. The lowest value of -0.07%/K was found for a doping of 10 ¹⁶ cm^-3, in accordance with theoretical predictions. High signal-to-noise ratios corresponding to minimal detectable fields of 50 nT/Hz^l/2 and 160 nT/Hz^l/2, respectively, were measured at 1 kHz and 100 Hz     

Electrical characteristics of 4.5 kV implanted anode 4H-SiC p-i-njunction rectifiers

4500 V 4H-SiC p-i-n junction rectifiers with low on-state voltage drop (3.3-4.2 V), low reverse leakage current (3×10^-6 A/cm²), and fast switching (30-70 ns) have been fabricated and characterized. Forward current-voltage measurements indicate a minimum ideality factor of 1.2 which confirms a recombination process involving multiple energy levels. Reverse leakage current exhibits a square root dependence on voltage below the punchthrough voltage where leakage currents of less than 3×10^-6 A/cm² are measured. Reverse recovery measurements are presented which indicate the presence of recombination at the junction perimeter where a surface recombination velocity of 2-8×10⁵ cm/s is found. These measurements also indicate drift layer bulk carrier lifetimes ranging from 74 ns at room temperature to 580 ns at 250°C     

Performance of PV HgCdTe arrays for 1-14-µm applications

Recent developments in HgCdTe epitaxial-growth techniques and device-surface passivation resulted in major performance improvements of photovoltaic infrared detectors. By utilizing CdTe substrates, thin HgCdTe layers are grown from the liquid phase with any desired composition, thereby yielding detector material with peak sensitivity that can be adjusted for a wavelength from 1 to 14 µm. Two approaches for junction formation are reported; implanted homojunction and double-layer heterojunction. Detectivity limited by background radiation (BLIP) is reported. Theoretically predicted values ofR_{0}Aare measured for diodes designed to cover the 1-3-, 3-5-, and 8-14-µm bands. The frequency and junction-bias dependence of the dark noise current are characterized at a level of 5 × 10^-15A/Hz^1/2. It is shown that the device performance at any wavelength and temperature of interest can be described in terms of generation-recombination (G-R) and diffusion of minority-carrier current mechanisms.     

Bias and temperature dependence of Sb-based heterostructure millimeter-wave detectors with improved sensitivity

Nearly lattice-matched InAs/AlSb/GaSb-based heterostructure backward diodes for zero-bias millimeter wave detection were fabricated and measured. A record-high curvature, /spl gamma/=39.1 V/sup -1/, at zero bias was measured. On-wafer sensitivity measurements from 1 to 110 GHz gave a record-high average sensitivity of 3687 V/W for zero-bias operation. Further enhancement of detector sensitivity was observed with applied dc bias, with a sensitivity of 7996 V/W obtained for a 0.9 /spl mu/A bias. Extrapolating the conjugately-matched measured sensitivity suggests that 1000 V/W should be achievable at a record-high 541 GHz. The temperature dependence of detector sensitivity was evaluated from measured dc current-voltage characteristics and gave expected sensitivities ranging from 3910 V/W at 293 K to 7740 V/W at 4.2 K.