Sheng S. Li

A metal grating coupled bound‐to‐miniband transition GaAs multiquantum well/superlattice infrared detector

We report here a new metal grating coupled top illumination, bound‐to‐miniband transition multiple quantum well/superlattice GaAs/AlGaAs long wavelength infrared detector. By using resonant tunneling and coherent transport along the superlattice miniband, at the same time increasing the effective barrier height of the quantum well and reducing the noise‐like charge transport higher energy bandwidth, a peak detectivity D* of 1.6×1010 cm√Hz/W at 8.9 μm and T= 77 K was obtained for this detector.

A voltage‐tunable multicolor triple‐coupled InGaAs/GaAs/AlGaAs quantum‐well infrared photodetector for 8–12 μm detection

A voltage‐tunable multicolor triple‐coupled quantum‐well infrared photodetector (TC‐QWIP) has been developed for 8–12 μm detection. The TC‐QWIP consists of three coupled quantum wells formed by an enlarged Si‐doped InxGa1−xAs quantum well and two undoped GaAs quantum wells separated by two thin AlyGa1−yAs barriers. Two TC‐QWIP structures with varying indium and aluminum compositions were designed and demonstrated. Due to the strong coupling effect of the asymmetrical quantum wells, three bound states (E1,u2009E2,u2009E3) are formed inside the quantum wells of the TC‐QWIP. The main detection peak wavelength is due to E1→E3 bound states transition for both devices, while two secondary detection peaks due to E1→E2 and E1→Ec continuum states transitions under different biases were also observed. In addition, a strong quantum‐confined Stark shift effect for the E1→E3 transition was observed in the wavelength range of 8.2–9.1 and 10.8–11.5 μm for QWIP‐A and QWIP‐B, respectively; both devices exhibit a linear dependence...

Low dark current step‐bound‐to‐miniband transition InGaAs/GaAs/AlGaAs multiquantum‐well infrared detector

A new step‐bound‐to‐miniband (SBTM) transition multiquantum‐well long‐wavelength infrared photodetector (LWIP) using a lightly strained In0.07Ga0.93As quantum well and a short‐period GaAs/Al0.4Ga0.6As superlattice barrier structure has been developed. The new structure created a potential ‘step’ in the superlattice barrier to block the undesirable electron tunneling current from the heavily doped ground state in the quantum well, which results in a significant reduction in the device dark current. The measured absorbance spectra and photocurrent are in good agreement with our theoretical predictions. The peak detectivity D* at λ=10.5 μm was found to be 2.1×1010 cm √Hz/W at Vb=5 V and T=63 K.

Determination of minority‐carrier diffusion length in indium phosphide by surface photovoltage measurement

The surface photovoltage technique has been employed to measure the hole diffusion length on three n‐type InP specimens. The hole diffusion length was found to be 1.8 μm for specimens with (111) orientation and 1.4 μm for specimens with (100) orientation. The measured hole diffusion length was found to be independent of the surface conditions.

Ultralow dark current p‐type strained‐layer InGaAs/InAlAs quantum well infrared photodetector with background limited performance for T≤100 K

An ultralow dark current normal incidence p‐type strained‐layer In0.3Ga0.7Al/In0.52Al0.48As quantum well infrared photodetector (PSL‐QWIP) grown on (100) semi‐insulating InP substrate by molecular beam epitaxy technique for 8–12 μm infrared detection was demonstrated for the first time. This PSL‐QWIP shows background limited performance (BLIP) for T≤100 K, which is the highest BLIP temperature ever reported for a QWIP. Due to a 1.5% lattice mismatch between the substrate and quantum well, a biaxial tensile strain was created in the In0.3Ga0.7As well layers. As a result, the light‐hole state becomes the ground state for the free hole with small effective mass. The dramatic increase of optical absorption can be attributed to the large in‐plane density of states and the small light‐hole effective mass as a result of heavy‐ and light‐hole state inversion. The dark current density and BLIP detectivity for this PSL‐QWIP were found to be 7×10−8 A/cm2 and 5.9×1010 cm−√Hz/W, respectively, at λp=8.1 μm, Vb=2 V, and...

Photovoltaic and photoconductive dual‐mode operation GaAs quantum well infrared photodetector for two‐band detection

A new photoconductive (PC) and photovoltaic (PV) dual‐mode operation quantum well infrared photodetection (DM‐QWIP) using an enlarged GaAs (110 A) quantum well and enlarged Al0.25Ga0.75As (875 A) barrier layer has been developed for two‐color intersubband detection. The detection scheme uses transitions from the ground‐state and the first excited‐state inside the enlarged GaAs quantum well to the continuum states slightly above the AlGaAs barrier layers. The detectivity Dλ* for the PV mode was found to be 1.5×109√Hz/ W at the peak response wavelength λp=7.7 μm and T=77 K, while the values of Dλ* for the PC mode were found to be 2×1010, 1×1010 cm√Hz/W for Vb=1,2 V at λp=12 μm and T=77 K, respectively.

The effect of compressive strain on the performance of p-type quantum-well infrared photodetectors

A detailed study of the performance of compressively strained p-type III-V quantum-well infrared photodetectors (p-QWIPs) is presented in this work. Three device structures composed of InGaAs-GaAs, InGaAs-AlGaAs, and InGaAs-AlGaAs-GaAs for normal incidence absorption have been fabricated and analyzed, with the results being compared with similar reported unstrained p-QWIPs. In all three QWIP structures, the quantum-well layers are under biaxial compressive strain ranging from -0.8% to -2.8%, while the barrier layers are lattice-matched to the substrate. The detection peaks of the quantum-well infrared photodetectors ranged from 7.4 to 10.4 /spl mu/m. The detectors utilized the bound-to-continuum, bound-to-quasi-bound, and step bound-to-miniband intersubband transitions for infrared detection. The results showed that responsivities of up to 90 mA/W and detectivities from 10/sup 9/ to over 10/sup 10/ cm/spl radic/Hz/W are achieved under moderate applied bias and at reasonable operating temperatures (from 60 to 80 K), demonstrating the viability of the strained-layer p-doped quantum-well infrared photodetectors for staring focal plane array applications.

Largely enhanced bound‐to‐miniband absorption in an InGaAs multiple quantum well with short‐period superlattice InAlAs/InGaAs barrier

We report for the first time, the intersubband absorption at 10.7 μm between the localized ground state and the global miniband state in an n‐type InAlAs/InGaAs multiple quantum well and short‐period superlattice barrier heterostructure. The use of enlarged quantum well width and the superlattice reinforced miniband structure has shown a significant enhancement in the net intersubband absorption. An integrated optical absorption strength of IA=19.5 Absu2009cm−1 was obtained under the Brewster’s incident angle at T=300 K, which is about five times larger than that of the conventional single bound‐to‐bound transition in the InAlAs/InGaAs quantum well structure.

Voltage-tunable dual-mode operation InAlAs/InGaAs quantum well infrared photodetector for narrow- and broadband detection at 10 μm

A new photoconductive (PC) and photovoltaic (PV) dual‐mode operation quantum well infrared photodetector using a lattice‐matched n‐type In0.52Al0.48As/In0.53Ga0.47As system has been developed for both the narrow‐band (Δλ/λp=7%) and broadband (Δλ/λp=24%) detection with a peak spectral response around λp=10 μm. The detection scheme utilizes a voltage‐tuned bound‐to‐miniband transition from the ground state in the In0.53Ga0.47As(110 A) quantum well to the global miniband states in the InAlAs/InGaAs superlattice barrier layers. The detectivity D*λ for the PV mode operation was found to be 5.7×109 cmu2009√Hz/W at λp=10 μm and T=67 K, while D*λ for the PC mode operation was found to be 5.8×109 √Hz/W at Vb =0.5 V, λp=10.3 μm, and T=67 K.

Investigation of multi-color, broadband quantum well infrared photodetectors with digital graded superlattice barrier and linear-graded barrier for long wavelength infrared applications

Abstract We report four different InGaAs/AlGaAs multi-color, broadband (BB) quantum well infrared photodetectors (QWIPs) with digital graded superlattice barrier (DGSLB) and linear-graded barrier (LGB) for long wavelength infrared (LWIR) detection. The two DGSLB-QWIPs were grown using compositionally DGSLB structures with GaAs/Al 0.15 Ga 0.85 As material system to create a staircase-like band gap variation in the barrier region. A BB spectral response (7–16 μm) was obtained under positive biases while a normal spectral response ( λ p =11 μm) was obtained under negative biases in the BB-DGSLB-QWIP. A high sensitivity double barrier (DB)-DGSLB-QWIP with a thin undoped Al 0.15 Ga 0.85 As DB grown on both side of the quantum well has also been studied. A normal spectral response with peak wavelength at 12 μm was obtained in this device under both positive and negative biases. In addition, two InGaAs/AlGaAs QWIPs using Al x Ga 1– x As LGB with and without AlGaAs DB layers have also been investigated. For the BB-LGB-QWIP, the BB spectral response was obtained under positive biases while the voltage-tunable multi-color detection with two peaks were obtained at negative biases. A very high responsivity was achieved in the DB-LGB-QWIP.