Chi-Shiang Hsu

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.

Effect of Growth Pressure of Undoped GaN Layer on the ESD Characteristics of GaN-Based LEDs Grown on Patterned Sapphire

The effect of growth pressure of underlying undoped GaN(u-GaN) layer on the electrical properties of GaN-based light-emitting diodes (LEDs) grown on patterned sapphire substrates (PSS) is evaluated. The electrostatic discharge (ESD) endurance voltages could increase from 4000 to 7000 V when the growth pressure of u-GaN layers is increased from 100 to 500 torr, while the forward voltages and light output powers remain almost the same. Poor ESD endurance ability could be attributed to the underlying GaN layer grown under relative low pressure, which leads to significant surface pits. This could be further attributed to the imperfect coalescence of crystal planes above the convex sapphire patterns. The pits are associated with TDs behaving as a leakage path to degrade electrical performance.

On a GaN-Based Light-Emitting Diode With an Indium–Tin–Oxide (ITO) Direct-Ohmic Contact Structure

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 Current-Spreading Performance of an InGaN-based Light-Emitting Diode with a Clear P-GaN/N-GaN Barrier Junction

The InGaN-based light-emitting diode (LED) with a clear 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 current crowding phenomenon yields the reduced parasitic effect. Therefore, under an injection current of 20 mA, improved behaviors including lower turn-on voltage, lower parasitic series resistance, and significantly enhanced electrostatic discharge (ESD) performance are presented.

Improved performance of GaN-based light-emitting diodes by using short-period superlattice structures

Abstract An InGaN/GaN multiple-quantum-well (MQW) light-emitting diode (LED) with a ten-period i (undoped) -InGaN/p (Mg doped) -GaN (2.5 nm/5.0 nm) superlattice (SL) structure, was fabricated. This SL structure that can be regarded as a confinement layer of holes to enhance the hole injection efficiency is inserted between MQW and p-GaN layers. The studied LED device exhibits better current spreading performance and an improved quality, compared with a conventional one without SL structure. Due to the reduced contact resistance as well as more uniformity of carriers injection, the operation voltage at 20 mA is decreased from 3.32 to 3.14 V. A remarkably reduced reverse-biased leakage current (10−7–10−9 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%, respectively. In addition, significant enhancement of 25.4% in output power as well as increment of 5% in EQE for the studied devices is observed, as the studied devices show superior current spreading ability and reduction in dislocations offered by the SL structure.

Comprehensive Temperature-Dependent Studies of Metamorphic High Electron Mobility Transistors With Double and Single

The temperature-dependent characteristics of meta morphic high electron mobility transistors (MHEMTs) with double and single δ-doped structure are studied and demonstrated. Due to the use of double δ-doped sheets, the current density in the channel layer and two-dimensional electron gas could effectively be increased. The excellent turn-on voltage of 1.18 (0.80) V, max imum drain saturation current of 544 (524) mA/mm, maximum extrinsic transconductance of 361 (312) mS/mm, unity current gain cutoff frequency of 55.06 GHz, and maximum oscillation frequency of 129.17 GHz are obtained at 300 (510) K for a 0.6 × 100 μm2 gate dimension double δ-doped MHEMT. In addition, using wide-bandgap InAlAs Schottky, spacer, and buffer layers, the carrier confinement could significantly be improved at high temperature. Therefore, excellent thermal stability is achieved for double δ-doped MHEMT. The device with a double δ-doped structure exhibits a considerably low temperature coefficient on threshold voltage (∂Vth/∂T) of 0.06 mV/K when the temperature is increased from 330 to 510 K, which is superior to previous reports of related high electron mobility transistors.

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The electrostatic discharge (ESD) characteristics of GaN-based light emitting diodes (LEDs) with textured p-GaN layers grown on c-axis vicinal sapphire substrates are studied and demonstrated. Based on the machine model, the device grown on a 0.35° tilt sapphire shows the highest ESD tolerance, whereas the one grown on a 0.2° tilt sapphire exhibits the poorest tolerance. This phenomenon is primarily influenced by the presence of maximum capacitance (C m ) values induced by a parasitic capacitance effect at the p-GaN/indium tin oxide interface rather than the difference in dislocation densities between LEDs.