Jiayi Shao

Low-strain InAs∕InGaAs∕GaAs quantum dots-in-a-well infrared photodetector

The authors report the design, growth, fabrication, and characterization of a low-strain quantum dots-in-a-well (DWELL) infrared photodetector. This novel DWELL design minimizes the inclusion of the lattice-mismatched indium-containing compounds while maximizing the absorption cross section by enabling larger active region volume. The improved structure uses an In0.15Ga0.85As∕GaAs double well structure with Al0.10Ga0.90As as the barrier. Each layer in the active region was optimized for device performance. Detector structures grown using molecular beam epitaxy were processed and characterized. This new design offers high responsivity of 3.9A∕W at a bias of 2.2V and a detectivity of 3×109 Jones at a bias of 2.2V for a wavelength of 8.9μm. These detectors offer significant improvement in the responsivity while retaining the long wave infrared spectral properties of the InAs∕In0.15Ga0.85As∕GaAs DWELL. These detectors if coupled with improved noise characteristics could enable higher temperature operation of ...

Reduction in dark current using resonant tunneling barriers in quantum dots-in-a-well long wavelength infrared photodetector

We report the use of resonant tunneling (RT) assisted barriers to reduce the dark current in quantum dots-in-a-well (DWELL) infrared photodetectors. Designed RT barriers allow energy-selective extraction of photoexcited carriers while blocking a continuum of energies. Over two orders of magnitude reduction in the dark current in the RT-DWELL device over a control sample without RT-DWELL at 77K has been demonstrated. Specific detectivity (D*) of 3.6×109cmHz1∕2W−1 at 77K at λpeak=11μm with a conversion efficiency of 5.3% was obtained in the RT-DWELL device. D* for the RT-DWELL device is five times higher than that of the control sample.

Resonant Tunneling Barriers in Quantum Dots-in-a-Well Infrared Photodetectors

The use of resonant tunneling (RT) barriers in the design of quantum dots-in-a-well (DWELL) infrared photodetectors is reported. The design of RT barriers for a variety of goals has been discussed. For simple DWELL designs, we demonstrate 2-3 orders-of-magnitude reduction in the dark current, with significant increase in the specific detectivity (D *) of the device. Two RT barriers are designed to selectively extract midwave and longwave components of the spectral response. We also report the use of RT barriers on strain-optimized quantum dots-in-a-double-well (DDWELL) structures to achieve very low dark current levels with peak D * of 2.9 ×1010 cm· Hz1/2 /W for a longwave infrared detection. Ability to select a particular wavelength in the spectral response is demonstrated with DDWELL architectures as well.

Quantum Dots-in-a-Well Focal Plane Arrays

In this paper, the basics and some of the recent developments in quantum dots-in-a-well (DWELL) focal plane arrays (FPAs) are reviewed. Fundamentally, these detectors represent a hybrid between a conventional quantum well infrared photodetector (QWIP) and a quantum dot infrared photodetector (QDIP), in which the active region consists of quantum dots (QDs) embedded in a quantum well (QW). This hybridization grants DWELLs many of the advantages of its components. These advantages include normally incident photon sensitivity without gratings or optocoupers, like QDIPs, and reproducible control over operating wavelength through ldquodial-in recipesrdquo as seen in QWIPs. Recently reported high-temperature operation results for DWELL FPAs now back up the conclusions drawn by the long carrier lifetimes observed in DWELL heterostructures using femtosecond spectroscopy. This paper will conclude with a preview of some upcoming advances in the field of DWELL FPAs.

Investigation of multistack InAs/InGaAs/GaAs self-assembled quantum dots-in-double-well structures for infrared detectors

The authors report the InAs/InGaAs/GaAs/AlGaAs quantum dots-in-double-well (D-DWELL) design, which has a lower strain per DWELL stack than the InAs/InGaAs/GaAs DWELLs thereby enabling the growth of many more stacks in the detector. The purpose of this study is to examine the effects of varying the number of stacks in the double DWELL detector on its device performance. The structures are grown by solid source molecular beam epitaxy on GaAs substrates. After fabrication of single pixel devices, a series of device measurements such as spectral response, dark current, total current, and responsivity were undertaken and the photoconductive gain and the activation energies were extracted. The goal of these experiments is not only to optimize the device performance by optimizing the number of stacks but also to investigate the transport properties as a function of the number of stacks.

Enhanced normal incidence photocurrent in quantum dot infrared photodetectors

The authors report an enhancement in the photocurrent caused by normal incidence (s-polarization) radiation in a quantum dot-in-a-well (DWELL) based infrared photodetector. The s-to-p polarization ratio was increased to 50%, compared to the 20% in conventional quantum dot (QD) detectors. This improvement was achieved through engineering the dot geometry and the quantum confinement via postgrowth capping materials of the QDs. The effect of the capping procedures was determined by examining the dot geometry using transmission electron microscopy (TEM) and s-to-p ratio of the polarized photocurrent in the DWELL infrared photodetector. The TEM image shows a quantum dot with a reduced base of 12 nm and an increased height of 8 nm. The infrared photodetector fabricated from this material shows peak photodetectivities of 1×109 cm Hz1/2/W at 77 K for a peak wavelength of 4.8 μm and 1×107 cm Hz1/2/W at 300 K for a peak wavelength of 3.2 μm. The dark current density is as low as 2×10−4 A/cm2 and the photoconductive...

Midwave infrared quantum dot avalanche photodiode

We report the first demonstration of a GaAs based avalanche photodiode (APD) operating in the midwave infrared region (3–5 μm). In the device, called the quantum dot avalanche photodiode, an intersubband quantum dots-in-a-well detector is coupled with an APD through a tunnel barrier. Using this approach, we have increased the photocurrent and reached a conversion efficiency of 12%, which is one of the highest reported conversion efficiencies for any quantum dot detector.

High Operating Temperature Quantum-Dot Infrared Photodetector Using Advanced Capping Techniques

We demonstrate an improvement in the operating temperature of a quantum dot-in-a-well (DWELL)-based infrared photodetector with spectral response observable till 250 K. This improvement was achieved through engineering the dot geometry and the quantum confinement via postgrowth capping of the quantum dots (QDs) by selecting overlying materials under various growth conditions. The effect of the capping procedures was determined by examining the optical properties of the QDs. These were then introduced into the active region of a DWELL IR photodetector. Using this approach, the dark current density is as low as 6.3 × 10^-7 A/cm² (V_b = 7 V) at 77 K; the highest operating temperature is increased to 250 K with the λ_p = 3.2 μm. The peak detectivity is found to be 1 × 10⁹ cm·Hz^1/2 /W at 77 K and 7.2 × 10⁷ cm·Hz^1/2/W at 250 K.

Increased normal incidence photocurrent in quantum dot infrared photodetectors

We have increased the ratio of s-polarization (normal incidence) to p-polarization photocurrent to 50% in a quantum dot-in-a-well based infrared photodetector form the typical s-p polarization ratio about 20%. This improvement was achieved by engineering the dot geometry and the quantum confinement via post growth capping materials of the Stranski Krastanov growth mode quantum dots (QDs). The TEM images show that the height to base ratio of shape engineered QDs was increased to 8 nm/12 nm from the control samples ratio 4 nm/17 nm. The dot geometry correlates with the polarized photocurrent measurements of the detector.

High Operating Temperature InAs Quantum Dot Infrared Photodetector via Selective Capping Techniques

We report on the improvement in a quantum dot-in-a-well (DWELL) - based infrared photodetectors operating temperature with spectral response observable till 150 K. This improvement was achieved through addressing issues related with the growth conditions and subsequent capping of the quantum dots (QDs) by various overlying materials. The influence of these conditions was determined by examining the size and optical properties of the QDs as well as how it affected their function as the absorbing region in a DWELL IR photodetector. Photoluminescence of InAs QDs embedded in asymmetric InGaAs/GaAs quantum well or AlGaAs/InAlGaAs quantum well with different capping materials and different growth temperatures have been characterized as a function of the intermixing energies between the interface of the QDs and the capping materials. Through the improvement in QD confinement, the dark current can be decreased and the overall temperature of operation can be increased to 150 K.