Yi-Jung Liu

On an AlGaInP-Based Light-Emitting Diode With an ITO Direct Ohmic Contact Structure

An interesting AlGaInP multiple-quantum-well light-emitting diode (LED) with a direct ohmic contact structure, formed by an indium-tin-oxide (ITO) transparent film and AuBe diffused thin layer, is fabricated and studied. The direct ohmic contact structure is performed by the deposition of an AuBe diffused thin layer and the following activation process on the surface of a Mg-doped GaP window layer. Experimental results demonstrate that a dynamic resistance of 5.7 Omega and a forward voltage of 1.91 V, under an injection current of 20 mA, are obtained. In addition, the studied LED exhibits a higher external quantum efficiency of 9.7% and a larger maximum light-output power of 26.6 mW. The external quantum efficiency is increased by 26% under the injection current of 100 mA, as compared with the conventional LED without this structure. This is mainly attributed to the reduced series resistance resulted from the relatively uniform distribution of AuBe atoms near the GaP layer surface and the effective current spreading ability by the use of ITO film. Moreover, the life behavior of the studied LED, under a 20-mA operation condition, is comparable to the conventional LED without this structure.

Performance investigation of GaN-based light-emitting diodes with tiny misorientation of sapphire substrates

GaN-based light-emitting diodes (LEDs) grown on c-plane vicinal sapphire substrates are fabricated and characterized. Based on the material quality and electrical properties, the LED with a 0.2 degrees tilt sapphire substrate (device A) exhibits the lowest defect density and high performance, while the LED with a 1.0 degrees tilt sapphire (device D) exhibits the highest one. At 2 mA, the extremely enhanced output power of 23.3% indicates of the reduction of defect-related nonradiative recombination centers in active layers for the device A. At 60 mA, the improved value is up to 45.7%. This is primarily caused by the formation of indium quantum dots in MQW which provides an increased quantum efficiency.

Characteristics of a GaN-Based Light-Emitting Diode With an Inserted p-GaN/i-InGaN Superlattice Structure

An interesting GaN-based light-emitting diode (LED) with a ten-period i (undoped)-InGaN/p (Mg doped)-GaN (2.5 nm/5 nm) superlattice (SL) structure, inserted between a multiple-quantum well (MQW) structure and a p-GaN layer, is fabricated and studied. This inserted SL can be regarded as a confinement layer of holes to enhance the hole injection efficiency. As compared with a conventional LED device without the SL structure, the studied LED exhibits better current spreading performance and an improved quality. The turn-on voltage, at 20 mA, is decreased from 3.32 to 3.14 V due to the reduced contact resistance as well as the more uniformity of carriers injection. A substantially reduced leakage current (10- 7 to 10- 9 A) and higher endurance of the reverse current pulse are found. The measured output power and external quantum efficiency (EQE) of the studied LED are 13.6 mW and 24.8%. In addition, as compared with the conventional LED without the SL structure, the significant enhancement of 25.4% in output power as well as the increment of 5% in EQE are observed due to the superior current spreading ability and reduction of dislocations offered by the SL structure.

On a GaN-Based Light-Emitting Diode With a p-GaN/i-InGaN Superlattice Structure

An interesting GaN-based light-emitting diode (LED) with a ten-period i-InGaN/p-GaN (5-nm/5-nm) superlattice (SL) structure, inserted between a multiple-quantum-well structure and a p-GaN layer, is fabricated and studied. This inserted SL can be regarded as a confinement layer of holes to enhance the hole injection efficiency. As compared with a conventional LED device without the SL structure, the studied LED exhibits better current-spreading performance and an improved quality. The turn-on voltage, at 20 mA, is decreased from 3.32 to 3.14 V due to the reduced contact resistance as well as the more uniformity of carrier injection. A substantially reduced leakage current (10-7-10-9 A) and higher endurance of the reverse current pulse are found. As compared with the conventional LED without the SL structure, the significant enhancement of 25.4% in output power and the increment of 5% in external quantum efficiency are observed.

Implementation of an indium-tin-oxide (ITO) direct-Ohmic contact structure on a GaN-based light emitting diode

A GaN-based light-emitting diode (LED) with a direct-Ohmic contact structure, formed by an indium-tin-oxide (ITO) transparent film and Au thermal-diffused and removed layer, is studied. By depositing an Au metallic film on the Mg-doped GaN layer followed by thermal annealing and removed processes, an ITO direct-Ohmic contact at p-GaN/ITO interface is formed. An enhanced light output power of 18.0% is also found at this condition. This is mainly attributed to the larger and more uniform light-emission area resulted from the improved current spreading capability by the use of an ITO direct-Ohmic contact structure.

Improved Performance of an InGaN-Based Light-Emitting Diode With a p-GaN/n-GaN Barrier Junction

An InGaN-based light-emitting diode with a p-GaN/n-GaN barrier junction is fabricated and investigated. Due to the built-in potential induced by this junction, superior current spreading performance is achieved. In addition, the suppression of the current-crowding phenomenon yields a reduced parasitic effect. Therefore, under an injection current of 20 mA, improved behaviors, including lower turn-on voltage, lower parasitic series resistance, and reduced p-n junction temperature, are achieved. In addition, due to the improved current-spreading ability, longer life-time, driving at medium current injection (60 mA), as well as significantly enhanced electrostatic discharge performance, are obtained.

UV Enhanced Field Emission Performance of Mg-Doped ZnO Nanorods

Vertical Mg-ZnO nanorods were synthesized on glass substrates using a low-temperature hydrothermal method. The field emission performance of Mg-ZnO nanorods was greatly enhanced by UV light illumination. It was found that the Mg-ZnO nanorods grown at 80 °C were structurally uniform and well oriented with pure wurtzite structure. Mg-ZnO nanorod exhibited turn-on fields was 2.27 V/μm, and field enhancement factors (β) was 2212. UV illumination of the Mg-ZnO nanorod reduced the turn-on electrical field from 2.27 to 1.97 V/μm and enhanced the β from 2212 and 4136.

Visible-Blind Photodetectors With Mg-Doped ZnO Nanorods

In this letter, Mg-doped ZnO nanorods were fabricated successfully on a glass substrate at 80°C by hydrothermal method. The visible-blind photodetectors show good stability properties in ultraviolet (UV) illumination. The resulting Mg-doped ZnO nanorods have excellent potential for application in a UV photodetector because of Mg-doped ZnO nanorods UV photodetector has a high UV-to-visible ratio, fast rise/fall time. The dynamic response of the Mg-doped ZnO nanorods photodetector with Au electrodes was stable and reproducible with an on/off current contrast ratio of ~ 5.2×103.

Characteristics of an AlGaInP-Based Light Emitting Diode With an Indium-Tin-Oxide (ITO) Direct Ohmic Contact Structure

An AlGaInP multi-quantum-well (MQW) light-emitting diode (LED) with a direct Ohmic contact structure, formed by an indium-tin-oxide (ITO) transparent film and AuBe diffused thin layer, is fabricated and studied. By the deposition of an AuBe metallic thin layer on the surface of Mg-doped GaP window layer, followed by a thermal activation process, a direct Ohmic contact between ITO and p-GaP layers can be obtained. Experimentally, under an injection current of 20 mA, a dynamic resistance of 5.7 ¿ and a forward voltage of 1.91 V, are obtained. In addition, a higher external quantum efficiency of 9.7% and a larger maximum light output power of 26.6 mW are found for the studied LED. As compared with the conventional LED without this structure, the external quantum efficiency of the studied device is increased by 26% under the injection current of 100 mA. This is mainly attributed to the reduced series resistance resulted from the relatively uniform distribution of AuBe atoms near the GaP layer surface and the effective current spreading ability by the use of ITO film. Moreover, the life behavior is not degraded by using this AuBe diffused layer for the studied LED under a 20 mA operation condition.

On the Pseudomorphic High Electron Mobility Transistors (PHEMTs) With a Low-Temperature Gate Approach

The characteristics of AlGaAs/InGaAs/GaAs depletion-mode (D-mode) and enhancement-mode (E-mode) pseudomorphic high electron mobility transistors (PHEMTs) fabricated using an electroless-plated (EP) deposition approach are investigated. Under the low-temperature and low-energy conditions, the EP deposition approach can form a better metal-semiconductor interface. For the studied devices, with a 1times100 mum2 gate dimension, excellent characteristics of the maximum drain saturation current (168.9 mA/mm) and extrinsic transconductance (225.8 mS/mm) are obtained for the D-mode device. The corresponding values for the E-mode device are 152.5 mA/mm and 211.7 mS/mm, respectively. Moreover, the EP approach also has the advantages of easy operation and low cost.