J. Chu

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...

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.

Investigation of broad-band quantum-well infrared photodetectors for 8-14-/spl mu/m detection

Typical quantum-well infrared photodetectors (QWIPs) exhibit a rather narrow spectral bandwidth of 1-2 /spl mu/m. For certain applications, such as spectroscopy, sensing a broader range of infrared radiation is highly desirable. In this paper, we report the design of four broad-band QWIPs (BB-QWIPs) sensitive over the 8-14-/spl mu/m spectral range. Two n-type BB-QWIPs, consisting of three and four quantum wells of different thickness and/or composition in a unit cell which is then repeated 20 times to create the BB-QWIP structure, are demonstrated. The three-well n-type In/sub x/Ga/sub 1-x/As-Al/sub y/Ga/sub 1-y/As BB-QWIP was designed to have a response peak at 10 /spl mu/m, with a full-width at half-maximum (FWHM) bandwidth that varies with the applied bias. A maximum bandwidth of /spl Delta//spl lambda///spl lambda//sub p/=21% was obtained for this device at V/sub b/=-2 V. The four-well n-type In/sub x/Ga/sub 1-x/As-GaAs BB-QWIP not only exhibits a large responsivity of 2.31 A/W at 10.3 /spl mu/m and V/sub b/=+4.5 V, but also achieves a bandwidth of /spl Delta//spl lambda///spl lambda//sub p/=29% that is broader than the three-well device. In addition, two p-type In/sub x/Ga/sub 1-x/As-GaAs BB-QWIPs with variable well thickness and composition, sensitive in the 7-14-/spl mu/m spectral range, are also demonstrated. The variable composition p-type BB-QWIP has a large FWHM bandwidth of /spl Delta//spl lambda///spl lambda//sub p/=48% at T=40 K and V/sub b/=-1.5 V. The variable thickness p-type BB-QWIP was found to have an even broader FWHM bandwidth of /spl Delta//spl lambda///spl lambda//sub p/=63% at T=40 K and V/sub b/=1.1 V, with a corresponding peak responsivity of 25 mA/W at 10.2 /spl mu/m. The results show that a broader and flatter spectral bandwidth was obtained in both p-type BB-QWIPs than in the n-type BS-QWIPs under similar operating conditions.

A normal incidence two‐color p‐type compressive strained‐layer In0.4Ga0.6As/GaAs quantum well infrared photodetector for 3–5 μm and 8–12 μm detection

A normal incidence p‐type compressive strained‐layer In0.4Ga0.6As/GaAs quantum well infrared photodetector (PSL‐QWIP) grown on (100) semi‐insulting GaAs substrate with molecular beam epitaxy technique for 3–5 μm mid‐wavelength infrared and 8–14 μm long‐wavelength infrared detection was demonstrated for the first time. This PSL‐QWIP shows a broadband double‐peak response between 8 and 9 μm wavelength by utilizing the resonant transport coupling mechanism between the heavy‐hole type‐I states and the light‐hole type‐II states. Using the compressive strain in the InGaAs quantum well, normal incident absorption was greatly enhanced by reducing the heavy‐hole effective mass and increasing density of states of off‐zone center. Maximum responsivities of 93 mA/W and 30 mA/W were obtained at peak wavelengths of λp1=8.9 μm and λp3=5.5 μm, respectively, with Vb=1.6 V. Detectivity at λp1=8.9 μm was found to be 4.0×109 cm√Hz/W at Vb=0.3 V and T=75 K.

INVESTIGATION OF BROADBAND P-TYPE QUANTUM-WELL INFRARED PHOTODETECTORS

Typical quantum-well infrared photodetectors (QWIPs) exhibit rather narrow spectral bandwidths of 1–2 μm. For certain applications, such as spectroscopy, sensing of a broad range of infrared photons is necessary. In this letter, we report on the design of two p-type broadband (BB) QWIPs for detection in the 7–14 μm long-wavelength infrared band. Two different QWIP structures were designed: QWIP-A with three wells of different InxGa1−xAs(x=0.2,0.25,0.3) compositions and QWIP-B with three wells of In0.25Ga0.75As of different thicknesses (4.5, 5.5, and 6.2 nm) and an undoped GaAs barrier (40 nm thick) to form a unit cell, which are then repeated 20 times to create the BB-QWIPs. The spectral response for QWIP-A covers the wavelengths from the 7 to 11 μm range, while QWIP-B has a broader spectral response bandwidth from 7 to 14 μm. A maximum responsivity of 25 mA/W was obtained for QWIP-B at Vb=1.1 V, λp=10.2 μm, and T=40 K with a spectral bandwidth of Δλ/λ=63%, a cut-on wavelength at 6.2 μm, and a cut-off wav...

Investigation of Si-doped p-type AlGaAsGaAs, AlGaAsInGaAs quantum well infrared photodetectors and multiquantum wells grown on (3 1 1)A GaAs

Abstract We have studied two Si-doped p-type quantum well infrared photodetectors (QWIPs) using AlGaAs GaAs and AlGaAs InGaAs grown on (3 1 1)A GaAs. The Si-doped AlGaAs GaAs p-QWIP exhibits a symmetrical dark I–V characteristic at all the measured temperatures from 40 to 120 K. The strained p-type AlGaAs InGaAs QWIP exhibits a slightly asymmetrical dark I–V characteristic, but is markedly less asymmetrical than that doped with beryllium. The slight asymmetry in dark I–V characteristic and the large blue-shift in responsivity spectra may be due to the thickness modulation observed from TEM and the red-shift of PL peak energy, where PL peak energies from (3 1 1)A AlGaAs InGaAs multiple quantum wells are red-shifts of 7 and 22 meV to the side-by-side grown (1 0 0).

Broadband quantum well infrared photodetectors

Typical quantum well infrared photodetectors (QWIPs) exhibit rather narrow spectral bandwidth of 1 to 2 micrometer. For certain applications, such as spectroscopy, sensing of a broader range of infrared radiation is highly desirable. In this work, we report the design of five broadband (BB-) QWIPs sensitive over the 7 to 14 micrometer spectral range. Three n- type BB-QWIPs consisting of three, four, and five quantum wells of different thickness and/or composition in a unit cell, which are then repeated 20 times for the three and four quantum wells (QW) devices and 3 times for the five QWs device to create the BB-QWIP structures, are demonstrated. The three- well n-type InxGa1-xAs/AlyGa1-yAs BB-QWIP is designed to have a response peak at 10 micrometer, with a FWHM bandwidth that varies with the applied bias. A maximum bandwidth of (Delta) (lambda) /(lambda) p equals 21% was obtained for this device at Vb equals -2 V. The four- well n-type InxGa1-xAs/GaAs BB-QWIP not only exhibits a very large responsivity of 2.31 A/W at 10.3 micrometer and Vb equals +4.5 V, but also achieves a broader bandwidth of (Delta) (lambda) /(lambda) p equals 29% than the three-well device. The five-well n-type InxGa1- xAs/GaAs BB-QWIP has achieved a FWHM bandwidth of (Delta) (lambda) /(lambda) p equals 28% at Vb equals 1.75 V. In addition, two p-type InxGa1-xAs/GaAs BB-QWIPs with variable well thickness and composition, sensitive in the 7 - 14 micrometer spectral range, are also demonstrated. The variable composition p-type BB-QWIP has a very large FWHM bandwidth of (Delta) (lambda) /(lambda) p equals 48% at Vb equals -1.5 V and T equals 40 K. The variable thickness p- type BB-QWIP was found to have an even broader FWHM bandwidth of (Delta) (lambda) /(lambda) p equals 63% at Vb equals 1.1 V and T equals 40 K, with a corresponding peak responsivity of 25 mA/W at 10.2 micrometer. The results reveal that p-type BB- QWIPs have a broader and flatter spectral bandwidth but lower responsivity than that of n-type BB-QWIPs under similar operating conditions.

The growth and characterization of two new p-type compressively strained layer InGaAs/AlGaAs/GaAs quantum well infrared photodetectors for mid- and long-wavelength infrared detection

Investigation of two p-type compressively-strained layer (PCSL) InGaAs/AlGaAs/GaAs quantum well infrared photodetectors (QWIPs) grown on (10 0) semi-insulating (SI) GaAs substrate has been carried out. The first detector uses a step-bound-to-miniband (SBTM) transition scheme for long wavelength infrared (LWIR) detection and has a detection peak at 10.4 μm with a full width at half-maximum bandwidth, Δλ/λ p = 20%. A responsivity of 28 mA/W was obtained for this detector at T = 65 K and V = 3.0 V, with a spectral detectivity D* = 1.4 x 10 9 cm Hz 1/2 W -1 at T = 65 K and V = 1.0 V. The detector was under the background limited performance (BLIP) at T = 40K and V ≤ 2.0 V. The second detector is a two-color stacked QWIP composed of a PCSL In 0.2 Ga 0.8 As/Al 0.3 Ga 0.7 As QWIP for the MWIR detection at λ p = 4.8 μm and a PCSL In 0.15 Ga 0.85 As/Al 0.1 Ga 0.9 As for the LWIR detection at λ p = 10 μm. The peak responsivity for the LWIR QWIP was found to be 25 mA/W at V b = 2 V, T = 40 K, λ p = 10 μm, a FWHM of Δλ/λ p = 40%, and the calculated detectivity was found to be D* = 1.1 x 10 10 cm Hz 1/2 W -1 . Two response peaks for the MWIR QWIP were found to be at 4.8 and 5.4 μm with maximum responsivities of 12 and 19 mA/W (at T = 77 K and V b = 5 V), and spectral bandwidths of 21 and 26%, respectively. The detectivity (D*) for the MWIR stack determined at λ p = 5.4 μm, V b = 1.0 V and T = 77 K was found to be 5.5 x 10 11 cm Hz 1/2 W -1 .

A new compressively strained‐layer p‐type InGaAs/AlGaAs/GaAs step bound to miniband quantum well infrared photodetector with a detection peak at 10.4 μm

Investigation of a InGaAs/AlGaAs/GaAs p‐type step bound‐to‐miniband compressively strained layer quantum well infrared photodetector grown on (100) semi‐insulating GaAs has been made. A long wavelength infrared detection peak at 10.4 μm with a full width at half‐maximum bandwidth, Δλ/λp=20% was obtained for this detector. The measured spectral peak is in good agreement with our theoretical prediction. A responsivity of 28 mA/W was obtained at T=65 K and V=3.0 V, with a spectral detectivity D* of 1.4×109 cm√Hz/W at T=65 K and V=1.0 V. The detector was under the background limited performance condition at T=40 K and V≤2.0 V.

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 percent, while the barrier layers are lattice matched to the substrate. The detection peaks of the quantum well infrared photodetectors ranged from 7.4 micrometers to 10.4 micrometers . 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 109 to over 1010 cm (root) Hz/W are achieved under moderate applied bias and at reasonable operating temperatures, demonstrating the viability of the strained layer p-doped quantum well infrared photodetectors for staring focal plane array applications.