Construction of a photon drag detector for evaluating the performance of a CO2 laser amplifier

In this article, the construction of P-type germanium (Ge) photon drag detector which is used to characterize the gain and output powers of a 10 W CO₂ laser and a CO₂ laser amplifier is described. Gain and laser amplifier output power versus laser input power measurements collected at 4.7 mbar and 12.0 mbar amplifier tube pressures are discussed. Moreover, measurements relating the CO₂ laser output power to the laser tube discharge current are provided at 6.9 mbar and 7.3 mbar tube pressures.     

Improving the performance of a far-infrared quantum-ring-based photodetector utilizing asymmetric multi-barrier resonant tunneling

In this paper, a novel structure for quantum ring inter-subband photodetectors (QRIP) is proposed to reduce its dark current. Some additional layers including asymmetric multi-barrier resonant tunneling (AMBRT) in absorption region layers are exploited to provide near unity tunneling probability for generated photocurrents and completely reject thermally generated electrons. AMBRT structure consists of three asymmetric AlGaAs barriers and two InGaAs wells which are designed for operation wavelength of generated photocurrents by absorption of 20 μm. Simulation results show that AMBRT can considerably reduce the dark current compared to previously proposed resonant tunneling structure about three orders of magnitude. As a consequent, higher specific detectivity for AMBRT-QRIP is obtained in the order of ∼10¹¹ cm Hz^1/2/W at 100 K.     

Analysis and evaluation of uniformity of SWIR InGaAs FPA—Part I: Material issues

The nonuniformity caused by fluctuations of indium composition, thickness and doping concentration of epitaxial absorption layer of InGaAs focal plane arrays (FPAs) is estimated theoretically with the incorporation of practical status. By the measurements on epitaxy wafers of 2 in. size, the fluctuation of indium composition is observed to be less than ±0.2% and ±1% for lattice matched In_0.53Ga_0.47As and wavelength extended In_0.80Ga_0.20As photodetector structures respectively, while the thickness and doping fluctuations are assumed to be the same. Results show that the response nonuniformity caused by fluctuation of indium composition is dependent on the target wavelength and can be neglected with a minor composition fluctuation if the cutoff wavelength is well set. The total response nonuniformity induced by the effects of thickness and doping fluctuations, which dominates the FPA performance for large signal applications, is estimated to be less than ±0.1% and ±0.5% for In_0.53Ga_0.47As and In_0.80Ga_0.20As FPAs smaller than 1 in. in maximum side length. Neglecting the effects of defects, the total detectivity nonuniformity caused by these fluctuations is about ±2% for In_0.53Ga_0.47As FPA and will reach up to about ±19% for In_0.80Ga_0.20As FPA, where the dark current nonuniformity due to the fluctuation of composition plays the most critical role.     

大气背景下盖革模式APD激光雷达探测性能计算

盖革模式工作的雪崩光电二极管,以其灵敏度高著称,广泛应用于天文观测、粒子物理学、激光雷达以及通信领域.但是由于雪崩光电二极管易受到噪音的影响,特别是在背景光较亮的白天,背景噪音对探测有很大影响.本文针对白天大气背景噪音的情况,建立了盖革模式雪崩光电二极管的探测统计模型,通过设定不同探测器阈值和噪音值进行仿真计算,分析了探测阈值与噪音对虚警率的影响,给出了提高最远探测距离的途经与方法.通过限制滤光片带宽、减小探测器开启时间等方法可以将背景噪音光子数减小到2,在900km处的探测成功率为96.6%.对雷达散射截面为1m2的非合作目标,探测成功率为70%.     

An infrared pyroelectric detector improved by cool isostatic pressing with cup-shaped PZT thick film on silicon substrate

In this paper, we presented a new pyroelectric detector with back to back silicon cups and micro-bridge structure. The PZT thick film shaped in the front cup was directly deposited with designed pattern by electrophoresis deposition (EPD). Pt/Ti Metal film, which was fabricated by standard photolithography and lift-off technology, was sputtered to connect the top electrode and the bonding pad. The cold isostatic press (CIP) treatment could be applied to improve the pyroelectric properties of PZT thick film. The infrared (IR) properties the CIP-optimized detector were measured. The voltage responsivity (R_V) was 4.5 × 10² V/W at 5.3 Hz, the specific detectivity (D^*) was greater than 6.34 × 10⁸ cm Hz^1/2 W⁻¹ (frequency > 110 Hz), and the thermal time constant was 51 ms, respectively.     

石墨炔修饰的ZnO薄膜紫外探测器

制备了石墨炔修饰的金属-半导体-金属结构的ZnO紫外探测器,研究了不同旋涂次数的石墨炔修饰对探测器性能的影响。实验结果表明,石墨炔修饰的探测器比未修饰器件的光电流提高4倍,暗电流降低2个数量级,同时探测器的响应度和探测率也明显提高,其中旋涂2次的石墨炔修饰的器件特性为最优。在10 V偏压下,旋涂2次的石墨炔修饰的探测器响应度高达1759 A·W⁻¹,探测率高达4.23× 10¹⁵ Jones,这是迄今为止报导过的溶胶-凝胶法制备的ZnO紫外探测器的最高值。经过对探测器各项性能的测试分析可知,石墨炔修饰的ZnO探测器性能的提高归因于石墨炔良好的空穴传输特性。暗环境下ZnO与石墨炔界面处形成p-n结,使探测器的暗电流大幅降低;光照条件下光生空穴在石墨炔中聚集,减少了电子空穴对的复合,有效提高了器件的光电流。由于石墨炔修饰减少了ZnO表面的氧分子吸附和解吸附过程,器件的响应速度也明显加快。     

Modeling and analysis of photoconductive detectors based on Hg<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te for free space optical communication

In this paper we report a theoretical analysis of a long wavelength photoconductive detector for characterizing and optimizing the device in respect of voltage responsivity, quantum efficiency, detectivity and noise equivalent power. The model has been applied to examine the potential of an n-type Hg_0.77Cd_0.23Te photoconductive detector for possible application in free space optical communication system operating at the atmospheric window near 9.6 μ m. In the present analysis we have taken into account all the major recombination mechanisms (e.g., Radiative, Auger, and Shockley-Read-Hall types) including the effect of surface recombination at the interfaces that shape the characteristics of photoconductor. The results obtained on the basis of our analysis reveal that in the absence of surface recombination the device exhibits a peak quantum efficiency of 90%, a maximum detectivity of 10⁸ MHz^1/2/W at 77 K, a 3 dB bandwidth of 117.86 MHz and noise voltage of 5.4 × 10⁻⁶ V/Hz^1/2. The sweep-out effect has been found to degrade the detectivity nearly by a factor of 10 at the same temperature and wavelength of operation. The estimated noise equivalent power of the photodetector is of the order of 10⁻⁹ W at 9.6 μm wavelength.     

Analytical Simulation of an InAsSb Photovoltaic Detector for Mid-Infrared Applications

A generic model of a mid-infrared photodetector based on a narrow bandgap semiconductor has been developed. The model has been applied for analysis and simulation of an InAs_0.89Sb_0.11 photovoltaic detector for operation at room temperature in 2–5 μm wavelength region. The model takes into account the effect of tunneling and other components of dark current on the detectivity of the device by considering all the three dominant recombination mechanisms e.g., radiative, Shockley-Read-Hall and Auger recombination. The study revealed that the dark current of the photodetector under reverse bias is dominated by trap-assisted tunneling component of current and this causes the detectivity of the device to decrease at high reverse bias. It is further concluded that by operating the device at a suitable low reverse bias it is possible to improve the room-temperature detectivity significantly as compared to its value at zero bias.     

Ultra-high detectivity room temperature THZ-IR photodetector based on resonant tunneling spherical centered defect quantum dot (RT-SCDQD)

In this paper, a novel structure for THZ-IR photodetector based on resonant tunneling spherical centered defect quantum dot (RT-SCDQD) operating at room temperature is proposed. The proposed structure includes a quantum dot with centered defect following a resonant tunneling double barrier. It is shown that inserting a centered defect leads to considerable enhancement in absorption coefficient at long wavelength in small dot size (1.05 × 10⁶-7.33 × 10⁶ m⁻¹ at 83 μm). This effect guarantees large responsivity of the proposed system for THZ-IR photodetector. In this proposal, intersublevel transitions in related states positioned at mid energies of large conduction-band-offset materials (GaN/AlGaN) are used to depress the thermal effect in dark current. Adding the resonant tunneling double barrier to the quantum dot resolves the basic problem of collecting electrons from deep excited state without applying large bias voltage. Also, employing the RT double barrier reduces the ground state dark current term. Reduction of the dark current and increasing the responsivity yields ultra-high detectivity, 5 × 10¹⁶ and 2.25 × 10⁹ cm Hz^1/2/W at 83 μm, at 83 and 300 K, respectively. Analysis of the proposed structure is done analytically.     

Nanostructures with Ge–Si quantum dots for infrared photodetectors

In this paper questions of optimization of growth conditions in the method of molecular beam epitaxy for creation of high-efficient quantum dot infrared photodetectors are considered. As a model material system for theoretical investigations, heterostructures with germanium-silicon quantum dots on the silicon surface are chosen. For calculations of the dependencies of quantum dots array parameters on synthesis conditions the kinetic model of growth of differently shaped quantum dots based on the general nucleation theory is proposed. The theory is improved by taking into account the change in free energy of nucleation of an island due to the formation of additional edges of islands and due to the dependence of surface energies of facets of quantum dots on the thickness of a 2D wetting layer during the Stranski–Krastanow growth. Calculations of noise and signal characteristics of infrared photodetectors based on heterostructures with quantum dots of germanium on silicon are done. Dark current in such structures caused by thermal emission and barrier tunneling of carriers, as well as detectivity of the photodetector in the approximation of limitation by generation-recombination noises are estimated. Moreover, the presence of dispersion of quantum dots by size is taken into account in the calculations of the generation-recombination noises. Results of calculations of the properties of structures with quantum dots and their dependencies on growth parameters, as well as the characteristics of quantum dot photodetectors are presented. Comparison of the estimated parameters of quantum dots ensembles and the characteristics of quantum dot photodetectors with experimental data is carried out.