Tung-Hsun Chung

Enhanced Normal-Incident Absorption of Quantum-Dot Infrared Photodetectors With Smaller Quantum Dots

Ten-period InAs-GaAs quantum-dot (QD) infrared photodetectors grown under different In adatom supply procedures are investigated. Two In adatom supply procedures of In shutter 1) always opened and 2) periodically opened/closed are adopted in this letter. Larger QD sizes in both height and diameter and more uniform size distribution are observed for samples grown under an In shutter periodically opened/closed condition. The device with QDs grown under the In shutter always opened condition has revealed shorter detection wavelengths and enhanced normal incident absorption. The phenomenon shows that beside the increase of energy difference between confinement states, smaller QD sizes would also enhance the normal incident absorption predicted for the theoretically zero-dimensional QD structures.

In-Plane Gate Transistors Fabricated by Using Atomic Force Microscopy Anode Oxidation

An in-plane gate transistor fabricated by using the atomic force microscopy (AFM) lithography is investigated in this letter. By performing repeated oxidation and deoxidation procedures by using the AFM for four times, two V-shaped trenches are fabricated on the prepatterned mesas to isolate the electrical terminals of the device. Without exposing the channel region to the atmosphere, the device has exhibited standard transistor current-voltage characteristics in the 0-5 V range at room temperature, which may be advantageous for the future high-speed application of the device.

In-Plane Gate Transistors With a 40-

An in-plane gate transistor with a GaAs/AlGaAs 2-D electron-gas channel about 40 μm in width is investigated. The saturation region and the drain current modulation at different gate bias voltages are observed despite the wide channel. The surface-induced channel depletion is suggested as the main mechanism for the turn-off of the drain current at - 10 V gate bias.

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Atomically-flat surfaces are obtained after thin GaAsSb buffer layer growth on GaAs substrates with regular-distributed nano-holes formed after oxide desorption of the local atomic-force-microscopy anode oxidation. Different from the samples with GaAsSb buffer layers, increasing surface root-mean-square roughness is observed for the GaAs-buffered samples with increasing GaAs buffer layer thickness. The phenomenon is attributed to the enhanced adatom migration resulting from the incorporation of Sb atoms. By using the substrates with nano-holes after buffer layer growth, site-controlled self-assembled InAs quantum dots (QDs) are observed with the deposition of a below-critical-thickness InAs coverage of 1.3 monolayer (ML).

-Wide Channel Width

This study explores the growth and effects of a ten-period InAs∕GaAs quantum-dot infrared photodetector (QDIP). With a uniform quantum-dot (QD) size distribution and a QD density of 2.8×1010cm−2, this 10K photoluminescence spectrum shows a peak energy at 1.07eV and a narrow full width at half maximum of 31.7meV. The QDIP exhibits an asymmetric response under different voltage polarities and a high responsivity of 1.7A∕W at −1.1V. Another noticeable observation in the spectral response of the device is the 6μm peak detection wavelength with a high spectral broadening Δλ∕λ of 0.67. By analyses of the photoluminescence excitation spectrum and the temperature dependence of spectral response, the wide spectral response of the QDIP is attributed to the summation of transitions between QD excited states and the wetting layer states, instead of transitions between QD ground state and higher excited states.

Site-controlled self-assembled InAs quantum dots grown on GaAs substrates

In this article, the authors investigate the influences of different InAs coverages on the photoluminescence excitation (PLE) spectra and spectral responses of InAs/GaAs quantum-dot infrared photodetectors (QDIPs). An increase in InAs coverage would lead to an increase in energy separation between heavy-hole state and light-hole state in the wetting layer (WL) region in the QD PLE spectra. The results suggest that most of the strain resulted from the InAs/GaAs lattice mismatch may be accumulated in the WL instead of the QD region. Also observed are the similar energy separations of energy levels responsible for the intraband absorption in the PLE spectra of the QDIPs such that similar detection wavelengths are observed for the devices.

The transition mechanisms of a ten-period InAs∕GaAs quantum-dot infrared photodetector

The influence of preoxidation GaAs surface treatment over the atomic force microscopy-induced local anodic oxidation (LAO) is investigated in this paper. By immerging the GaAs samples into NaOH aqueous solutions, higher nano-oxides with better height distribution could be observed after LAO. The phenomenon is attributed to the hydrophilic surfaces obtained after the treatment such that higher local humidity and uniform water molecular distribution would be obtained on the GaAs surfaces, by using the higher nano-oxides with better height uniformity, nanomesas by using wet chemical etching, and nanometal contact after oxide lift-off are fabricated.

Transition mechanism of InAs/GaAs quantum-dot infrared photodetectors with different InAs coverages

In this article, we report the growth of InAs∕GaAs quantum dots (QDs) grown under different As4-supply procedures. The growth of the investigated samples carried out by the three procedures of As shutter always opened, As shutter initially opened, and As shutter initially closed. The samples grown by the former two approaches show a uniform QD distribution and the multiple-peak luminescence, which correspond to ground-state, first-excited-state, and second-excited-state luminescence, while that grown by the latter only shows large InAs islands. The results suggest that the As-stabilized condition at the initial stage of QD growth is very critical for the high-quality QD formation.