Effects of a p–n junction on heterojunction far infrared detectors

HEterojunction Interfacial Workfunction Internal Photoemission (HEIWIP) far infrared detectors based on the GaAs/AlGaAs material system have shown promise for operation at wavelengths up to a few hundred microns. HEIWIP detectors with GaAs emitters have been shown to operate out to 92 μm. Recent modifications to use AlGaAs emitters have extended the zero response threshold out to 128 μm. Extension to longer wavelengths will require reducing the dark current in the devices. An approach using the addition of a p–n junction in the detector, which was shown to work in QWIP and homojunction detectors is considered here. Differences between the predicted and observed threshold behavior could be explained by the presence of space charge within the device. The band bending from this space charge produces the observed variation in the threshold. The space charge can also be used to explain anomalous conduction observed at low biases. When the device is forward biased, the current is expected, to be small until the bias voltage is similar to the bandgap of 1.4 eV, above which the current should increase rapidly. Dark current was observed for biases significantly less than the bandgap. The threshold bias decreased with temperature, and was as low as 0.25 V for a temperature of 300 K. This is much lower than could be explained by thermal effects alone.     

Nonlinear level crossing in the infrared transitions of optically pumped far infrared laser media

In conjunction with the Stark field induced power enhancement in optically pumped far infrared lasers, absorption transitions in a degenerate two level system under the influence of an weak static Stark field have been analyed. A third order theory to the density matrix formalism leads to zero field level crossing signals for absorption in rate equation approximation and in Doppler limit. For fast relaxation among Zeeman sublevels, the zero field level crossing signal arises from population effect. Optoacoustic measurements have been carried out on the ₅,^qQ(16,8) absorption line of CH₃OH which produces the familiar 119-m laser with the CO₂ 9P(36) pump line. The optoacoustic absorption signals observed are well reproduced by the theoretical expression.     

可用于红外探测器的自组织量子线及其带间和子带间光学跃迁

研究了自组织量子线Ga1-xInxAs的结构、应力分布及其光学性质.模拟了微应力导致的横向成序及其导引短周期超晶格形成量子线的过程，并计算出量子线在原子尺度上的微应力分布.这里考虑了价带各向异性、带间混合及局域应力分布对光学性质的作用.研究发现自组织量子线具有应用于正入射红外探测器的良好光学特性.结果显示当量子线的周期长度为15到30nm时，导带子带间跃迁波长处在10到20μm，这正是红外探测器的理想工作范围.同时，带间吸收波长在中红外范围，它提供了红外探测器的另一个窗口. 关键词： 自组织 微应力 红外探测器 量子线     

Influence of the Sb dopant distribution on far infrared photoconductivity in Ge:Sb blocked impurity band detectors

Extended long wavelength response to 200 μm (50 cm⁻¹) has been observed in Ge:Sb blocked impurity band (BIB) detectors with N_D1×10¹⁶ cm⁻³. The cut-off wavelength increases from 150 μm (65 cm⁻¹) to 200 μm (50 cm⁻¹) with increasing bias. The responsivity at long wavelengths was lower than expected. This can be explained by considering the observed Sb diffusion profile in a transition region between the blocking layer and active layer. BIB modeling is presented which indicates that this Sb concentration profile increases the electric field in the transition region and reduces the field in the blocking layer. The depletion region consists partially of the transition region between the active and blocking layer, which could contribute to the reduced long wavelength response. The field spike at the interface is the likely cause of breakdown at a lower bias than expected.     

The far infrared complex reflectivity of GaTe

The room temperature polarized complex (amplitude and phase) infra-red reflection spectra of single crystal monoclinic GaTe have been measured between 20 and 400 cm^–1 using a dispersive Fourier transform spectrometer. The measurements allow the experimental zone centre transverse and longitudinal phonon modes and optical constants to be determined without recourse to oscillator fit models or Kramers-Kronig analysis. Infrared power transmission measurements have allowed all fifteen predicted modes to be identified and the results are compared to recent Raman work.     

The far infrared optical constants of GaP

The FIR optical constants of GaP have been determined on either side of the Reststrahlen band by single pass transmission dispersive Fourier transform spectroscopy. These results extend the range of measured refractive index data for GaP, and reveal the dispersion in the refractive index in regions of weak absorption. Features in the spectrum are assigned as phonon combination bands with the aid of a critical point analysis based on phonon frequencies calculated using an 11-parameter rigid ion model.     

The far infrared optical constants of polyethylene

The optical constants of high and low density polyethylene have been determined in the far infrared spectral region between 50 and 450 cm⁻¹ at a temperature of 293 K.     

孔栅斜置对远场的影响

应用光波叠加原理,通过数值计算方法,分析了孔栅斜置对远场测量的影响。结果表明：孔栅斜置带来附加位相差,导致了远场分布与通常的孔栅竖直放置的不同,给光强(从而功率、光束质量等)的测量带来系统误差。孔栅平面越偏离竖直面,影响越大,且对衍射级越大的光斑的影响也越大。在设计和使用孔栅时,应选取较小的偏离角;在进行功率、光束质量等参数诊断时应选取低级次的衍射斑。     

The far infrared continuum absorption of water vapour

The far infrared transmittance of H₂O has been measured in the laboratory. A gas correlation radiometric technique was adopted for comparison with atmospheric H₂O measurements made by the Stratospheric and Mesospheric Sounder on Nimbus 7. Atmospheric paths were simulated in a multipass cell containing pure H₂O and H₂O + N₂ mixtures at various pressures and temperatures. A spectral transmittance model was developed using the simple Lorentz line shape and the HITRAN molecular line database and was compared with the transmittance measurements. The self-broadened continuum absorption, spectrally averaged over a passband centred at 7.85 THz (262 cm^-1), was determined and confirmed the continuum model of Clough et al. The foreign-broadened continuum was smaller by a factor of at least 19.     

The suppression of charged-particle-induced noise in infrared detectors

Charged-particle-induced noise in photoconductive detectors is discussed. A spike suppression circuit is described and observational performance data are presented.     

The comparison of ZnO nanowire detectors working under two wavelengths of ultraviolet

Schottky-barrier ultraviolet (UV) detectors based on ZnO-nanowires (NWs) were fabricated with Pt as electrodes in this investigation. The ZnO NWs synthesized by the hydrothermal method were characterized by field-emission scanning electron microscopy (FE-SEM), Raman and PL spectroscopy. Photoelectric properties under 254 and 365 nm UV light were investigated. It is found that the photo-response properties of the devices under 365 nm UV light are better than those under 254 nm UV light, which is further illustrated by light transmission theory, energy-band diagram and absorption spectra. The results demonstrate that ZnO NWs detectors with selectivity to near-UV (NUV) light are promising candidates in photoelectric devices.     

红外光电探测器的激光损伤分析

分析了国内外有关红外光电探测器激光损伤阈值的大量测量数据。讨论了激光损伤探测器的机理以及目前尚未解决的问题。比较了高重复频率脉冲激光和连续波激光对探测器的损伤效果。分析表明 ,在相同平均功率的条件下 ,高重复频率脉冲激光与连续波激光相比 ,探测器损伤效果前者要比后者大得多     

The theory of multiple quantum-well GaAs-AlGaAs infrared detectors

The theory of multiple quantum-well GaAs-AlGaAs IR detectors based on the principle of quantum well photoionization is presented. The expression for the photoionization probability of the symmetric quantum-well is found to be exact in the effective mass approximation. Depolarization effects in the optical absorption spectra are discussed. We demonstrate that the depolarization shift of the spectrum maximum and its broadening lead to non-monotonic dependence of the photodetector detectivity on the electron concentration in wells in the background limited IR performance condition. The optimal factor of quantum-well filling, corresponding to the maximum of detectivity is rather small, and for the photoresistor with boundary wavelength λ₁ = 10 μm, is θ =0.10.We have also performed calculations for the concentration dependence of the transition temperature for background limited IR performance and found that for optimal concentrations it is about T = 83 K (for λ₁ = 10 μm). The lifetime of non-equilibrium electrons is determined by capturing processes into the wells accompanied by emission of polar optical phonons and is τ ≅ 2 × 10⁻¹¹ s. The gain, along with the photoresistor sensitivity, is maximal for structures with a single quantum well.     

Characterization of GaSb/InAs type II infrared detectors at very long wavelengths: carrier scattering at defect clusters

We report a systematic study into carrier scattering by isovalent defects within GaSb/InAs superlattices. The heterostructure system which we investigate has attracted recent interest as the active region of a photodetector for very long wavelength infrared (VLWIR) (12 μm) radiation. To achieve our objective, we employed models of the electronic band structure and scattering cross-section. We considered isolated, substitutional defects at each atom site throughout the unit cell in turn and found that the scattering magnitude generally follows the carrier envelope function, being greatest where the overlap of charge with the defect is highest. We scrutinized the contribution of lattice relaxation around defects to the overall scattering, by comparing calculations where this effect was, in turn, included and excluded. We identified some anomalous contributions of relaxation to both qualitative and quantitative features of the cross-section. Physical mechanisms to explain these effects must be arrived at in order to attain satisfactory characterization of these materials, highlighting the need for both microscopic models and further research. Additional modelling of islands of such defects indicated that the cross-section is proportional to the square of the number of constituent atoms, for both carrier types (holes and electrons) and each defect type. This article demonstrates important links between key growth issues and the dynamical properties of these novel semiconductor devices.     

Optical properties of barite in the infrared and far infrared ranges

Far infrared and infrared reflectivity was measured for barite single crystal using polarized light. Twenty six oscillators were observed. The real and imaginary parts of the complex dielectric function were obtained by a fitting procedure for three directions (E a;E b andE c). Group theory analysis has been done in detail and the number and position of experimentally observed infrared active modes were compared with the theoretical predictions.     

Vectorial structure of Hermite–Laguerre–Gaussian beam in the far field

Starting from Maxwell's equations, a Hermite–Laguerre–Gaussian (HLG) beam is decomposed into the TE and TM terms by using the vector angular spectrum representation. By means of the method of stationary phase, the analytical TE and TM terms are presented in the far field. The energy flux distributions of the TE and TM terms are also investigated and depicted in the far field. The influences of the additional angle parameter and Gaussian waist width on the vectorial structure and energy flux pattern of HLG beam are also investigated. This research reveals the internal vectorial structure of HLG beam and may provide a new approach to the manipulation of laser beams.