Shu-Han Chen

Room-temperature operation type-II GaSb/GaAs quantum-dot infrared light-emitting diode

A GaSb/GaAs quantum-dot light-emitting diode (QD LED) with a single GaSb QD layer is investigated in this paper. The room-temperature photoluminescence peak blueshift with increasing excitation power densities suggests a type-II alignment of the GaSb/GaAs heterostructures. Significant electroluminescence (EL) is observed for the device under forward biases, which suggests that pronounced dipole transitions occur at the GaSb/GaAs interfaces. With increasing forward biases, the observed EL peak blueshift confirms that the origin of luminescence is from the type-II GaSb/GaAs QD structures. A model is established to explain the operation mechanisms of the type-II QD LED.

Influence of as on the Morphologies and Optical Characteristics of GaSb/GaAs Quantum Dots

The influence of As atoms on the morphologies of GaSb quantum dots (QDs) is investigated. Without any special treatment, GaSb quantum rings (QRs) are observed in the embedded GaSb layer even when the uncapped layer reveals QD like morphologies. With intentional As supply after the uncapped GaSb QD deposition, a QD to QR transition is observed. The phenomenon suggests that insufficient Sb atoms on the GaSb QDs would lead to the QD to QR transition as in the case of embedded GaSb layers. With extended Sb soaking time following GaSb deposition, QD structures could be well maintained for the embedded GaSb layers. A light-emitting diode operated at room temperature is fabricated based on the GaSb/GaAs QD structure. Identical peak positions in photoluminescence and electroluminescence (EL) spectra of the device show that type-II GaSb QDs are responsible for the observed EL.

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.

Graphitic carbon film formation under Ni templates by radio-frequency sputtering for transparent electrode applications

An alternate approach to the preparation of transfer-free graphitic carbon films is proposed in this paper. Using a standard radio-frequency sputtering system and a high-temperature annealing procedure, graphitic carbon films are prepared under Ni templates. The results demonstrate that carbon precipitation occurs at both Ni template interfaces. With repeated annealing procedures at 1100 °C, a sheet resistance of 1.36 × 104 Ω/□ can be achieved. Selective carbon film deposition has also been developed via pattern formation on the Ni templates. The results indicate the potential application of this method to transparent electrode formation.

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

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).

GaSb/GaAs quantum dots with type-II band alignments prepared by molecular beam epitaxy for device applications

The growth procedures and device applications of GaSb/GaAs quantum dots (QDs) are investigated in this report. The influence of As flux on the GaSb QD morphologies and optical characteristics has revealed the importance of precise Sb/As flux control during Sb post-soaking procedures after GaSb deposition. With optimized GaSb QD growth conditions and long-term Sb post soaking procedure, room-temperature operation light-emitting diodes (LEDs) and high-temperature operation quantum-dot infrared photodetectors (QDIPs) are demonstrated. The results have revealed the possibilities of type-II GaSb QDs in the applications of optical devices.