Harshal Rawool

AuGe surface plasmon enhances photoluminescence of the InAs/GaAs bilayer quantum dot heterostructure

We report an improvement in the photoluminescence of a GaAs-capped InAs/GaAs bilayer quantum dot (QD) heterostructure by AuGe nanoparticle deposition on the surface of a thin capped layer. Scanning electron microscopy confirmed the formation of AuGe nanoparticles on the surface at temperatures ranging from 300 to 700 °C. Optical absorption spectroscopy revealed the plasmon resonance peak of AuGe nanoparticles at around 670 nm for the sample annealed at 300 °C, confirming the presence of the plasmonic effect. Raman spectroscopy revealed a QD phonon peak at ∼238.5 cm−1 for the sample annealed at 300 °C, indicating InAs QDs in the heterostructure. Compared to the uncovered sample, enhancements were observed in the PL spectra of the AuGe-deposited samples annealed at 300 °C and 400 °C (with enhancement factors of 2.58 and 2.18, respectively). The observed enhancement is attributed to photon trapping by scattering from the cross section of the dipole radiation field. Increasing the annealing temperature from 300 °C to 700 °C blue-shifted the photoluminescence peaks at 18 K because of In/Ga inter-diffusion. A decrease in activation energy was observed with the increase in annealing temperature from 300 °C to 700 °C, attributed to poor confinement potential and high electron concentration at the sample surface. Our findings contribute to the realization of high-efficiency plasmonic-based InAs QD detectors for optical communication in the 1300 nm optical window.

Short wave infrared photodetector using p-i-p quantum dots (InAs/GaAs) for high temperature operation

In this study, we report high temperature operation of infrared photodetector using p-i-p InAs/GaAs quantum dots. The ground state emission peak at 18 K from photoluminescence spectroscopy was measured at 986 nm. Single pixel detectors were fabricated and device characteristics like temperature dependent dark current, blackbody and spectral response were analyzed. The measured dark current density at 220 K with applied bias of 0.2 V was 2.48×10-3 A/cm2. The spectral response peak (2 μm) was observed in short wave-infrared (SWIR) region. We report an excellent SWIR detection characteristics at 220 K with a responsivity and specific detectivity of 3.81 A/W and 2.18×1010 cmHz1/2/W, respectively. The spectral response peak was achieved till 250 K and blackbody signal was observed till 270 K.

Impact of varying barrier thickness on the optical characteristics of multilayer InAs/GaAs QDIPs

An investigation of the optical properties of the multi stacked InAs quantum dot (QD) based photodetectors has been done by changing the capping layer composition and thickness. There is an improvement obtained in the structure and distribution of InGaAs capped QDs than the conventional GaAs capped QDs. It is due to the inhibition of In-Ga intermixing and lesser indium segregation towards the wetting layer in case of InGaAs capping. Here, the combined InGaAs/GaAs capping layer thickness has been varied to investigate the effect of the vertical strain-coupling and QD size distribution. All samples are grown by solid source molecular beam epitaxy with a V/III flux ratio of 50. A variation in InGaAs/GaAs capping layer is done by keeping the total thickness constant at 12 nm, and 18 nm. The ground state photoluminescence emission peak for the 3 nm InGaAs capped QDs have pronounced redshift than the 2 nm InGaAs capped QDs. However, the redshift is more in case of total capping layer thickness of 12 nm (i. e. 36 nm), than the 18 nm capped sample (i. e. 14 nm). It is observed due to better coupling in case of lower capping layer thickness and hence better dot size. Activation energy calculated from the temperature dependent photoluminescence study also gives incremental trend with an increase in coupling (18nm: 163.308meV, and 12nm: 215.53meV), which is attributed to lowering of QD ground state due to change in capping layer thickness. Hence the 12nm capped device with 3nm InGaAs capping gives better results probably due to better strain propagation, and hence better dot distribution.

Design and Fabrication of 320 × 256 Focal-Plane Array Using Strain-Coupled Quaternary Capped InAs/GaAs Quantum Dots Infrared Photo-Detectors for Thermal Imaging

We report the fabrication and characterization of a 320 × 256 infrared focal-plane imager fabricated using an strain-coupled quaternary capped InAs quantum dots heterostructure, which showed multiple photoluminescence peak and activation energy of 207.38 meV for dominant peak. Multiple ground state peaks in photoluminescence spectra indicates multimodal dot size distribution which was confirmed using cross-sectional transmission microscopy images. We discuss the fabrication and characterization of single-pixel detectors that can measure intersubband spectral responses with peak intensity at 6.9 µm and narrow spectral linewidth of 19%. The highest detectivity of 2.48 × 1010 cm Hz1/2/W at 77 K was observed from proposed structure. Using the fabricated device, infrared images were captured at 50–100 K. Device optimization led to approximately 95% of the pixels in the imaging array being operational and a reasonably low noise equivalent temperature of approximately 0.080 °C at 100 K.

Enhancement in device performance of hepta-layer coupled InGaAs quantum dot infrared detector by AuGe surface plasmons

In this work, we have studied the effect of AuGe alloy nanoparticles deposition on properties of molecular beam epitaxy grown heptalayer coupled InGaAs 5.25 mono-layer quantum-dots (QDs) samples. AuGe 12 nm film was deposited using electron beam evaporator on these samples which were later annealed at 300 °C to create AuGe nanoparticles. SEM measurement confirms formation of AuGe nanoparticles which support surface Plasmon modes. The PL spectra at 20K confirms maximum enhancement of 53% in intensity of peak at ̴̴ 1123 nm for 300 °C annealed sample in comparison to as-grown (without nanoparticle) sample. Single pixel detectors were fabricated from asgrown and 300°C annealed nanoparticle sample using two level lithography and wet etching process. We have observed two-order and one-order augmentation in responsivity and detectivity from device having nanoparticles compared to the as-grown respectively at 80K. Peak detectivity of 4.2×107cm.Hz 1/2/W at 80K was observed for device having nanoparticles. Around 30% increment in spectral response having peak around 5μm at -1V bias for device having AuGe nanoparticles compared to the as-grown device was observed. The observed enhancement is due to increase light trapping or light scattering into the device by nanoparticles. Demonstration of this plasmonic-based detector will move forward the development of high-performance infrared QDs detectors.