Resonant-cavity-enhanced photodetectors and LEDs in the mid-infrared

In this paper we outline the use of resonant-cavity enhancement for increasing the exterior coupling efficiency of photodetectors and light-emitting diodes (LEDs) in the mid-infrared (MIR) spectral region. This method is potentially very important in the MIR because encapsulation is not presently feasible due to the lack of suitable materials. Among other potential applications, resonant-cavity-enhanced (RCE) photodetectors and LEDs could be particularly suitable for greenhouse gas detection because of their ‘pre-tunable’ spectrally narrowed resonantly enhanced peaks. We also present the optical characterization of an InAs RCE photodetector aimed at the detection of methane gas (λ≈3.3 μm), and an InAs/InAs_0.91Sb_0.09 resonant-cavity LED (RCLED) aimed at carbon dioxide gas (λ≈4.2 μm). The high peak responsivity of the RCE photodetector was 34.7 A/W at λ=3.14 μm, and the RCLED peaked at λ=3.96 μm. These are among the longest operating wavelengths for III–V RCE photodetectors and RCLEDs reported in the literature.     

SCN掺杂提高CsPbI3胶体量子点的稳定性和光探测性能

无机卤化物钙钛矿CsPbI₃胶体量子点因其优越的光电性能在光伏和发光器件领域中表现出极大的发展前景。然而,CsPbI₃较差的稳定性阻碍了实际应用。为此,我们采用SCN?离子掺杂CsPbI₃(SCN-CsPbI₃)量子点用于提高量子点的光学性能和稳定性。研究表明,SCN?离子掺杂不仅减少了量子点缺陷、改善了光学性能,还提高了Pb-X键能、量子点结晶质量以及钙钛矿结构稳定性。结果表明,SCN-CsPbI₃量子点的荧光量子产率(PLQY)超过90%,远高于未掺杂原始样品(PLQY为68%)。高的荧光量子产率表明量子点具有较低的缺陷态密度,这归咎于缺陷的减少。空间限制电荷和时间分辨荧光光谱等研究也证实SCN?离子掺杂减少了量子点的缺陷。此外,SCN-CsPbI₃量子点展现出很好的抗水性能,其荧光强度在水中浸泡4 h后依然保持85%的初始值。而未掺杂原始样品的荧光性能很快消失,这是因为水诱导其相变。基于SCN-CsPbI₃量子点的光电探测器表现出宽波域响应(400–700 nm),高的响应率(90 mA·W^?1)和超过1011 Jones的探测度,远高于未掺杂原始量子点探测器的性能(响应率为60 mA·W^?1和探测度为1010 Jones)。     

Design of a Resonant-Cavity-Enhanced p-i-n GaN/AlxGa1-xN Photodetector

A resonant-cavity-enhanced p-i-n photodetector has been designed and analyzed to operate at a wavelength of 360 nm based on the Al_xGa_1-xN material system. The novel approach has been adopted of using epitaxial AlN/Al_xGa_1-xN quarter-wave stacks as the distributed Bragg reflector that serves as the front mirror. An Al_xGa_1-xN absorptive filter layer is incorporated to suppress all but one resonant mode to ensure single, narrow-band operation. This device structure is projected to achieve wavelength selective, high speed, and high quantum efficiency operation in the ultraviolet. MOCVD-grown 6 1/2-pair AlN/Al_xGa_1-x     

Computer modeling of MWIR single heterojunction photodetector based on mercury cadmium telluride

In the present paper, an abrupt heterojunction photodetector based on Hg_1 − xCd_xTe (MCT) has been simulated theoretically for mid-infrared applications. A semi-analytical simulation of the device has been carried out in order to study the performance ratings of the photodetector for operation at room temperature. The energy band diagram, carrier concentration, electric field profile, dark current, resistance–area product, quantum efficiency and detectivity have been calculated and optimized as a function of different parameters such as device thickness, applied reverse voltage and operating wavelength. The effect of energy band offsets in conduction and valance band on the transportation of minority carriers has been studied. The influences of doping concentration, electron affinity gradient and the p–n junction position within heterostructure on potential barrier have been analyzed. The optical characterization has been carried out in respect of quantum efficiency, and detectivity of the heterojunction photodetector. In present model the Johnson–Nyquist and shot noise has been considered in calculation of detectivity. The simulated results has been compared and contrasted with the available experimental results. Results of our analytical-cum-simulation study reveal that under suitable biasing condition, the photodetector offers a dark current, I_D ≈ 6.5 × 10⁻¹² A, a zero-bias resistance–area product, R₀A ≈ 11.3 Ω m², quantum efficiency, η ≈ 78%, NEP = 2 × 10⁻¹² W Hz^1/2 and detectivity D^* ≈ 4.7 × 10¹⁰ mHz^1/2/W.     

GaN/AlN quantum dot photodetectors at 1.3–1.5 μm

We have demonstrated GaN/AlN quantum dots (QD) photodetectors, relying on intraband absorption and in-plane carrier transport in the wetting layer. The devices operate at room temperature in the wavelength range 1.3–1.5 μm. Samples with 20 periods of Si-doped GaN QD layers, separated by 3 nm-thick AlN barriers, have been grown by plasma-assisted molecular-beam epitaxy on an AlN buffer on a c-sapphire substrate. Self-organized dots are formed by the deposition of 5 monolayers of GaN under nitrogen-rich conditions. The dot height is 1.2±0.6 to 1.3±0.6 nm and the dot density is in the range 10¹¹–10¹² cm⁻². Two ohmic contacts were deposited on the sample surface and annealed in order to contact the buried QD layers. The dots exhibit TM polarized absorption linked to the s–p_z transition. The photocurrent at 300 K is slightly blue-shifted with respect to the s–p_z intraband absorption. The responsivity increases exponentially with temperature and reaches a record value of 10 mA/W at 300 K for detectors with interdigitated contacts.     

光敏层厚度与退火温度调控对聚3-己基噻吩光电探测器性能的影响

以聚3-己基噻吩(P3HT)为给体材料,富勒烯衍生物(PC61BM)为受体材料,制备了一系列结构为ITO/PEDOT:PSS/P3HT:PC61BM/C60/Al的体异质结光电探测器.研究了120、160、180与200 nm不同光敏层厚度,100、120、130、140与150℃不同退火温度等条件对器件性能的影响,并采用原子力显微镜(AFM)对光敏层形貌进行了分析.研究发现,基于180 nm厚光敏层、150℃退火处理的器件,在-2 V的偏压下550 nm处有最大响应度,为268 mA/W,并且在470~610 nm范围内响应度都超过了200 mA/W;基于180 nm厚光敏层、120℃退火处理的器件有最大线性动态范围,为95 dB.研究表明,适当厚度的光敏层有利于提高光吸收效率与器件的光伏性能;退火处理,可以使光敏层形成均匀的互穿网络结构,进而减小空穴与电子的复合概率,提高器件的光伏性能.     

CsPbBrI2量子点制备及其光探测器性能

采用热注入法制备空气稳定性良好的CsPbBrI2量子点,以375 nm的脉冲激光作为激发光源研究其光致发光性能.通过旋涂的方式制备相应薄膜,将其作为光敏层应用到光探测器,并对器件的光电子性能和稳定性进行详细研究.结果表明:CsPbBrI2量子点在635nm附近有强烈的荧光效应,光谱发光峰较窄,半峰宽约为35 nm.CsPbBrI2量子点禁带宽度为1.90eV,制备的探测器光检测带宽从紫外光260nm到红光650 nm,光响应度为0.26 A/W,高开/关比高达104,上升/衰减时间为3.5 ms/3.5 ms.在25℃,湿度在25%~35%大气环境下存储60天,性能与初始值相比几乎没有变化.CsPbBrI2量子点具有优异的稳定性、可制备高性能的宽带光检测和易于制造等优点,具备一定的应用前景.     

Improvement of frequency sensitivity of series photodetector frequency circuit system and its application for Cy5 fluorescence detection

This study elucidated the frequency characteristics of series photodetector frequency circuit system for detection of DNA probe ET996 marked with fluorescence dye Cy5. We developed 48 MHz series photodetector frequency circuit system with good sensitivity for fluorescence detection. In accordance with the theory of series photodetector frequency circuit system, the frequency sensitivity can be improved by adjusting circuit parameters such as A (tan θ), C_q, C₀, and C_p. In this research of A adjustment, the capacitance parameter C_m of 48 MHz series photodetector frequency circuit system was adjusted to improve the frequency sensitivity for detection of fluorescence dye concentration; moreover, the bias of photodetector was also adjusted to improve the frequency sensitivity. In the optimal conditions of capacitance match and photodetector bias, the detection limit of ET996-Cy5 fluorescence dye concentration 2 pmol/L can be measured by 48 MHz sensor system. The results of fluorescence experiment also demonstrated that the frequency shift of 48 MHz sensor system was linearly related to the logarithm of fluorescence dye concentration from 200 nmol/L to 2 pmol/L. The frequency method can be applied simply and the detection limit of ET996-Cy5 fluorescence dye concentration was lower than the conventional fluorescence technique by 2 orders.     

Simple approach to predict APD/PMT lidar detector performance under sky background using dimensionless parametrization

In this paper, we developed a simple approach to predict the APD/PMT (avalanche photodiode/photomultiplier) lidar detector performance in the presence of residual skylight background. By normalizing all relevant photodetector noise sources to the quantum noise, we obtain quantitative expressions for the degradation of the signal-to-noise ratio (SNR), the increasing threshold sensitivity of and decreasing lidar operation range. To apply the formalism to any lidar photodetectors operating in the ultra violet, visible and near-infrared spectral regions and to perform a comparative analysis of PMT and APD capabilities as the best photodetectors for ultra-violet (UV), visible (Vis) and near infra-red (NIR) lidar, we utilize a set of spectral characteristics that are built from an envelope of individual PMT and APD component responses. On this basis, the general analysis of system performance under intense background conditions is developed, and practical recommendations on detector use for each spectral region are given. The dimensionless formalism and the generalized detector spectral models used allows our analysis to be applied to nearly any lidar receiver operating over very different signal/background situations.     

Study of the Light Emitting Diode as a photoreceptor: Spectral and electrical characterization as function of temperature and lighting source

In this study, the temperature influence on the spectral responsivity of a Light Emitting Diode (LED) used as a photoreceptor, combined to light source spectrum is correlated to electrical characteristics in order to propose an alternative method to estimate LED junction temperature, regardless of the absolute illumination intensity and based on the direct correlation between the integral of the product of two optical spectra and the photo-generated currents. A laboratory test bench for experimental optical measurements has been set in order to enable any characterizing of photoelectric devices in terms of spectral behaviour, in a wavelength range placed between 400–1000?nm, and of current-voltage characteristics as function of temperature by using two different illumination sources. The temperature is analysed in a range from 5?°C up to 85?°C, so as to evaluate thermal variation effects on the sensor performance. The photo-generated current of two LEDs with different peak wavelengths has been studied. Research has observed and mathematically analysed what follows: since the photo-generated current strictly depends on the combination between the spectral response of the photoreceptor and the lighting source response, it becomes possible to estimate indirectly the junction temperature of the LEDs by considering the ratio between the photogenerated currents obtained by using two different illumination sources. Such results may for one thing increase knowledge in the fields where LEDs are used as photo-detectors for many applications and for another, they could be extended to generic photodetectors, thus providing useful information in photovoltaic field, for instance.