Enhancement of device performance by using quaternary capping over ternary capping in strain-coupled InAs/GaAs quantum dot infrared photodetectors

Abstract

We investigate and compare the performance of 30 layers strain-coupled quantum dot (SCQD) infrared photodetectors capped with one of two different layers: a quaternary (In 0.21 Al 0.21 Ga 0.58 As) or ternary (In 0.15 Ga 0.85 As) alloy of 30 Å and a GaAs layer with a thickness of 120-150 Å . Measurements of optical properties, spectral responsivity, and cross-sectional transmission electron microscopy were conducted. Results showed that quaternary capping yielded more superior multilayer QD infrared photodetectors than ternary capping. Quaternary capping resulted in enhanced dot size, order, and uniformity of the QD array. The presence of Al in the capped layer helped in the reduction in dark current density and spectral linewidth as well as led to higher electron confinement of the QDs and enhanced device detectivity. The vertically ordered SCQD system with quaternary capping exhibited higher peak detectivity (*10 10 cm Hz 1/2 /W) than that with ternary capping (*10 7 cm Hz 1/2 /W). In addition, a very low noise current density of *10 -16 A/cm 2 Hz 1/2 at 77 K was achieved with quaternary-capped QDs.

In-Situ Tailoring of Vertically Coupled InAs p-i-p Quantum-Dot Infrared Photodetectors: Toward Homogeneous Dot Size Distribution and Minimization of In–Ga Intermixing

“…Strain coupling between vertically spaced QD layers is one such approach that has been found to be particularly effective. , Uncoupled structures of SAQDs form random, small-sized dots with highly inhomogeneous size distribution which on integration into devices leads to undesirable results. In contrast, vertically coupled QDs have a greater dimension and better uniformity due to the propagation of strain from one layer to the next, which also enables them to interact both electronically and mechanically. , In the majority of the cases reported in the literature, vertical coupling of dots has yielded improved characteristics; however, these vertically stacked structures introduce some more shortcomings such as (i) interface roughness, (ii) threaded dislocation in the {111} plane, (iii) vertical threading dislocation, (iv) V-shaped dislocation, (v) poor crystallinity, etc. The close proximity of the dot layers owing to thin intermediate layers results in a high value of cumulative strain propagating in the heterostructures.…”

Impact of an InxGa1–xAs Capping Layer in Impeding Indium Desorption from Vertically Coupled InAs/GaAs Quantum Dot Interfaces

“…We have previously investigated the advantages of using quaternary capping over ternary capping in multistacked InAs QDs. 2,4 In addition, Mohanta et al have discussed the benefits of the carrier relaxation process for different spacer layer thicknesses in multistacked InAs QDs. 9 However, the VC structures also have some shortcomings that weaken the QD coupling.…”

“…Recently, vertical-coupled (VC) InAs/GaAs quantum dot (QD) heterostructures grown by molecular beam epitaxy (MBE) under the Stranski–Krastanov growth mode have shown a tremendous impact on the performance of optoelectronic devices such as solar cells, lasers, light-emitting diodes, IR detectors, and single-photon emitters. − In addition, the optical, structural, and electrical properties of three-dimensionally confined InAs QDs can be tuned over a wide range by designing various multistacked InAs QD heterostructures with different material compositions. The GaAs spacer layer thickness can also be tailored to achieve the desired emission wavelength .…”

“…These uncoupled QD structures degrade the optical quality of InAs/GaAs QD-based devices. Over the past years, extensive research has been carried out to improve the VC stacked structures by methods such as (i) optimizing the GaAs spacer thickness, (ii) introducing a strain-reducing layer, − (iii) varying the material composition of III–V semiconductor alloys of the strain-reducing layer, such as GaAs, InGaAs, , AlGaAs, , InAlGaAs, , GaAsSb, , and InGaAsSb, and (iv) varying the monolayer coverage for the seed-layer InAs QDs in order to achieve a high degree of correlation of vertically aligned QDs with stronger quantum confinement potential. We have previously investigated the advantages of using quaternary capping over ternary capping in multistacked InAs QDs. , In addition, Mohanta et al have discussed the benefits of the carrier relaxation process for different spacer layer thicknesses in multistacked InAs QDs .…”

Infrared photodetector sensitized by InAs quantum dots embedded near an Al0.3Ga0.7As/GaAs heterointerface

“…Since intraband transitions in QWs are forbidden for IR light normally incident on a QW slab (parallel to the sensor surface) according to the optical selection rule, QDs are more suited for realizing normal-incidence IR sensors. In particular, the application of InAs/GaAs QDs to QDIPs has been intensively studied [47][48][49][50][51][52][53][54] , because of the well-established growth of self-assembled QDs on GaAs substrates. The reported responsivity range of QDIPs enables detection of mid-wavelength IR (MWIR) light at 3 to 5 µm and long-wavelength IR (LWIR) light at 8 to 12 µm.…”