Long-Wavelength Quantum-Dot Infrared Photodetectors With Operating Temperature Over 200 K

We demonstrate the high-temperature operation of confinement enhanced dots-in-a-well (CE-DWELL) quantum-dot infrared photodetectors (QDIPs). The thin Al_0.3Ga_0.7As barrier layer added above the InAs QDs greatly improve the lateral confinement of QD states in the In_0.15Ga_0.85As DWELL structure and the device performance. With better device parameters of CE-DWELL, it is possible to achieve high quantum efficiency, high operating temperature, and long-wavelength detection at the same time.     

Single-Period InAs–GaAs Quantum-Dot Infrared Photodetectors

In this letter, we investigate the performance of single-period InAs–GaAs quantum-dot (QD) infrared photodetectors, in which the single-period QD is sandwiched by different thicknesses of the undoped GaAs confinement layers. By using a 5-nm p-type GaAs layer as a current blocking barrier, the investigated three devices exhibit no response, the highest response, and the medium response, respectively. It is attributed to three different electron occupancy situations in the QD region resulted from the various locations of the Fermi level. A higher barrier for the thermionic emission current is observed for the device with a lower Fermi level in the QD structure. It is attributed to the acceptor-like behavior of the depleted QD such that a higher barrier height would be observed.      

Enhanced Normal-Incident Absorption of Quantum-Dot Infrared Photodetectors With Smaller Quantum Dots

Ten-period InAs-GaAs quantum-dot (QD) infrared photodetectors grown under different In adatom supply procedures are investigated. Two In adatom supply procedures of In shutter 1) always opened and 2) periodically opened/closed are adopted in this letter. Larger QD sizes in both height and diameter and more uniform size distribution are observed for samples grown under an In shutter periodically opened/closed condition. The device with QDs grown under the In shutter always opened condition has revealed shorter detection wavelengths and enhanced normal incident absorption. The phenomenon shows that beside the increase of energy difference between confinement states, smaller QD sizes would also enhance the normal incident absorption predicted for the theoretically zero-dimensional QD structures.     

InGaAs/GaAs量子点红外探测器

与量子阱红外探测器相比,量子点红外探测器具有不制作表面光栅就能在垂直入射红外光照射下工作以及工作温度更高等优势。然而,目前阻碍量子点红外探测器性能提高的技术瓶颈主要来自组装量子点较差的大小均匀性、较低的量子点密度以及垂直入射下子带跃迁吸收效率低等原因。利用分子束外延技术研究了如何从量子点材料生长和器件设计两方面来克服这些困难,并且制作了几种不同结构的InGaAs/GaAs量子点红外探测器。 在77 K时,这些器件在垂直入射条件下观察到了很强的光电流信号。     

Quantum-Dot Infrared Photodetectors

We present a study of a series of n-i-n InAs quantum-dot infrared photodetectors (QDIPs) with unintentionally doped active regions. Different quantum-dot capping layer materials (GaAs, InGaAs, and AlGaAs) are utilized to tune the operating wavelength and modify the QDIP performance. Normal-incidence operation with high detectivity in the mid (3-5 ) and long (8-12 ) wavelength regimes and the potential for multicolor operation is demonstrated.     

Quantum Dot Based Infrared Focal Plane Arrays

In the past decade, there has been active research on infrared detectors based on intersubband transitions in self-assembled quantum dots (QDs). In the past two years, at least four research groups have independently demonstrated focal plane arrays based on this technology. In this paper, the progress from the first raster scanned image obtained with a QD detector to the demonstration of a 640 512 imager based on self-assembled QDs is reviewed. In particular, emphasis will be placed on a novel quantum dots-in-a-well (DWELL) design, which represents a hybrid between a conventional quantum-well infrared photodetector (QWIP) and a quantum-dot infrared photodetector (QDIP). In the DWELL detectors, the active region consists of InAs quantum dots embedded in an InGaAs quantum well. Like QDIPs, the DWELL detectors have 3-D confinement and display normal incidence operation while demonstrating reproducible ldquodial-in recipesrdquo for control over the operating wavelength, like QWIPs. Moreover, the DWELL detectors also have demonstrated bias-tunability and multicolor operation in the midwave infrared (MWIR, 3-5 ), long-wave infrared (LWIR, 8-12 ), and very long wave infrared (VLWIR, ) regimes. Recently midformat 320 256 and 640 512 focal plane arrays (FPAs) with an NETD of 40 mK at have been reported. The paper will conclude with a perspective on the future directions on the research on QDIP FPA including enhanced functionality and higher operating temperatures.     

Modulation-doped InAs-InGaAs quantum dot longwave infrared photodetector with high quantum efficiency

A modulation-doped InAs-InGaAs quantum dot (QD) longwave infrared photodetector (QDIP) is reported with a detection peak wavelength of 8.2 mum. The QDIP showed a high photoresponsivity of 0.8 A/W and a high quantum efficiency of 3.4% at the bias voltage of 0.4 V. The performance demonstration indicates that the modulation-doped QDIP is suitable for longwave infrared photodetection     

Quantum-Dot Semiconductor Mode-Locked Lasers and Amplifiers at 40 GHz

Mode-locked lasers (MLLs) and semiconductor optical amplifiers (SOAs) based on quantum-dot (QD) gain material will impact the development of next-generation networks, such as the 100 Gb/s Ethernet. MLLs presently consisting of a monolithic two-section device already generate picosecond pulse trains at 40 GHz. Temperature dependence of pulsewidth for p-doped devices, a detailed chirp analysis that is a prerequisite for optical time-division multiplexing applications, and data transmission experiments are presented in this paper. QD SOAs show superior performance for linear amplification as well as nonlinear signal processing. Using cross-gain modulation for wavelength conversion, QD SOAs are shown to have a small signal bandwidth beyond 40 GHz under high-bias current injection. This makes QD SOAs much superior to conventional SOAs.      

1.15-μm wavelength oxide-confined quantum-dot vertical-cavitysurface-emitting laser

Low-threshold lasing is achieved at 1.154 μm for an oxide-confined quantum-dot (QD) vertical-cavity surface-emitting laser (VCSEL) grown on a GaAs substrate. The long wavelength emission is obtained through use of an InAs-GaAs QD active region. A continuous-wave (CW) threshold of 502 μA is obtained for a device size of 10-μm diameter, corresponding to a threshold current density of 640 A/cm²      

Novel MIS Ge-Si quantum-dot infrared photodetectors

The metal-insulator-semiconductor (MIS) Ge-Si quantum-dot infrared photodetectors (QDIPs) are successfully demonstrated. Using oxynitride as gate dielectric instead of oxide, the operating temperature reaches 140 and 200 K for 3-10 and 2-3 /spl mu/m detection, respectively. From the photoluminescence spectrum, the quantum-dot structures are responsible for the 2-3 /spl mu/m response with high operation temperature, and the wetting layer structures may be responsible for the 3-10 /spl mu/m response. This novel MIS Ge-Si QDIP can increase the functionality of Si chip such as noncontact temperature sensing and is compatible with ultra-large scale integration technology.     

Comparison of Long-Wave Infrared Quantum-Dots-in-a-Well and Quantum-Well Focal Plane Arrays

This paper reports on a comparison between a commercially available quantum-well infrared focal plane array (FPA) and a custom quantum-dot (QD)-in-a-well (DWELL) infrared FPA in the long-wave infrared (LWIR). The DWELL detectors consist of an active region composed of InAs QDs embedded in $ hbox{In}_{.15}hbox{Ga}_{.85}hbox{As}$ quantum wells. DWELL samples were grown using molecular beam epitaxy and fabricated into 320 $times$ 256 pixels FPA with a flip-chip indium bump technique. Both the DWELL and QmagiQ commercial quantum-well detector were hybridized to an Indigo ISC9705 readout circuit and tested in the same camera system. Calibrated blackbody measurements at a device temperature of 60 K with LWIR optics yield a noise equivalent change in temperature of 17 mK and 91 mK for quantum-well and DWELL FPAs operating at 0.95- and 0.58-V biases, respectively. The comparison of the DWELL and quantum-well FPA when imaging a 35 $^{circ}hbox{C}$ black body showed that the DWELL had a signal-to-noise ratio of 124 while the quantum-well FPA showed 1961. As well, the quantum-well FPA showed a higher collection efficiency of 1.3 compared to the DWELL.      

GaAs0.7Sb0.3/GaAs type-II quantum-well laser with adjacent InAs quantum-dot layer

A GaAs_0.7Sb_0.3/GaAs type-II quantum-well laser with a InAs quantum-dot (QD) layer adjacent to the well is reported. The laser shows much lower threshold current density, lower internal loss and higher characteristic temperature than the device without adjacent QDs. The better performances are attributed to additional dimensional confinement, resulting from a spatial potential fluctuation induced by the adjacent QDs, for carriers in the active region of the laser.     

量子点红外光子探测器的研究进展

迄今为止关于量子点红外光子探测器（QDIP）的研究已有众多文献发表,涉及量子点生长、系统设训、建模、表征与测量等各方面,对近年来国外文献报道的QDIP技术的进展进行了总结和综述,简要描述了QDIP研发的方法和思路,给出了近期国外研制的一些QDIP的性能,介绍了今后实现高性能QDIP的若干发展方向,尽管QDIP已成功地用于单元探测器和焦平面器件,但作为一种新兴技术,QDIP仍不成熟,短期内直接替代HgCdTe似乎还不可能．     

CW Lasing at 1.35 $mu$m From Ten InAs–Sb : GaAs Quantum-Dot Layers Grown by Metal–Organic Chemical Vapor Deposition

We report the fabrication of GaAs-based quantum-dot (QD) lasers grown by metal-organic chemical vapor deposition (MOCVD) above 1.3 m. We fabricated a laser diode with ten stacked InAs-Sb:GaAs(100) QD layers, grown by antimony-surfactant-mediated growth. Ground-state lasing was obtained under continuous-wave operation at room temperature at 1.35 mum, with a maximum ground state modal gain of 19.3 cm^-1. These values are the highest values reported for MOCVD-grown GaAs-based QD laser.     

Threshold temperature dependence of lateral-cavity quantum-dotlasers

The threshold temperature dependence for quantum-dot (QD) lasers with different degrees of inhomogeneous broadening are compared. By reducing the inhomogeneous linewidth, the “negative” temperature dependence due to thermal coupling of the QD ensemble can be nearly eliminated, Stable ground state lasing is obtained with a single-layer QD density of -5×10¹⁰ cm^-2 for a long cavity laser, while lower gain QDs and shorter cavity lengths lase on well-resolved higher energy levels     

High-Speed Quantum-Dot Vertical-Cavity Surface-Emitting Lasers

We report on recent progress in high-speed quantum-dot (QD) vertical-cavity surface-emitting lasers (VCSELs). Advanced types of QD media allow an ultrahigh modal gain, avoid temperature depletion, and gain saturation effects. Temperature robustness up to 100degC for 0.96-1.25 mum range devices is realized in the continuous wave (cw) regime. An open eye 20 Gb/s operation with bit error rates better than 10^-12 has been achieved in a temperature range 25degC - 85degC without current adjustment. A different approach for ultrahigh-speed operation is based on a combination of the VCSEL section, operating in the CW mode with an additional section of the device, which is electrooptically modulated under a reverse bias. The tuning of a resonance wavelength of the second section, caused by the electrooptic effect, affects the transmission of the system. The approach enables ultrahigh-speed signal modulation. 60 GHz electrical and ~35 GHz optical (limited by the photodetector response) bandwidths are realized.     

Rate Equations for 1.3-$mu$ m Dots-Under-a-Well and Dots-in-a-Well Self-Assembled InAs–GaAs Quantum-Dot Lasers

A rate-equation model, in which three discrete quantum-dot (QD) energy levels are assumed and all possible relaxation paths and carrier transport in the GaAs barrier are considered, is presented to analyze the steady-state performance of 1.3 mum undoped and doped dots-under-a-well (DUW) and dots-in-a-well (DWELL) InAs-GaAs QD lasers. DWELL QD lasers have higher saturation value of QD level occupation probabilities and characteristic temperature (T₀) than that of DUW QD lasers due to the improvement of hole confinement. The p-doped QD laser shows lower threshold current density than n-doped QD laser at the same threshold condition, and the T₀ of n-doped DWELL laser is higher than that of p-doped DWELL laser at room temperature. Optimized QD layer number of DUW and DWELL QD lasers with different QD density is discussed     

Polarization Characteristics of Quantum-Dot Vertical-Cavity Surface-Emitting Laser With Light Injection

This investigation explores experimentally the optical characteristics of long-wavelength quantum-dot vertical-cavity surface-emitting lasers (QD VCSELs). The InAs QD VCSEL, fabricated on a GaAs substrate, is grown by molecular beam epitaxy with fully doped distributed Bragg reflectors. The optical characteristics of QD VCSEL without and with light injection are studied in detail. The QD VCSEL has the potential to be used in all-optical signal processing systems.      

量子点红外探测器的研究进展

量子点红外探测器（QDIP）在红外探测领域具有十分广阔的应用前景,同时由于QDIP的有效载流子寿命长、暗电流低、工作温度高、对垂直入射光响应等优势,近年来高性能QDIP已经成为研究的热点。文章首先简要介绍了QDIP的基本原理,然后重点介绍了目前国际上在提高QDIP性能方面的研究进展,分别从如何降低暗电流、实现多色探测、提高探测率等三个方面进行了讨论。     

Threshold Temperature Dependence of a Quantum-Dot Laser Diode With and Without p-Doping

A study of the threshold characteristics of quantum-dot (QD) laser diodes shows how inhomogeneous broadening and p-doping influence the QD laser's temperature dependence of threshold T ₀. The analysis includes the additional parameters of homogeneous broadening, quantum state populations, and threshold gain. The results show that while the source of negative T ₀ can occur due to different effects, the transparency current plays a critical role in both undoped and p-doped QD lasers. Experimental trends of negative T ₀ and their dependence on p-doping are replicated in the calculated results. Inhomogeneous broadening is found to play a lesser role to the transparency current in setting T ₀. Homogeneous broadening is most important for uniform QDs with thermally isolated ground-state transitions.