Ming-Shiou Lin

Chemical Lift-Off Process for Blue Light-Emitting Diodes

An epitaxial layer of an InGaN light-emitting diode (LED) structure was separated from a truncated-triangle-striped patterned-sapphire substrate through a chemical lift-off (CLO) process. A crystallographic stable and terminated V-shaped GaN grooved pattern was observed on the lift-off GaN surface. A peak wavelength blueshift phenomenon of the micro-photoluminescence spectrum was observed on the lift-off LED epitaxial layer (440.7 nm) compared with the LED/sapphire structure (445.8 nm). The free-standing LED epitaxial layer with a 453 nm electroluminescence emission spectrum was realized through a CLO process with the potential to replace the traditional laser lift-off process for vertical LED applications.

Blue light-emitting diodes with a roughened backside fabricated by wet etching

The InGaN-based light-emitting diodes (LEDs) with a roughened patterned backside on the N-face GaN surface were fabricated through a crystallographic etching process to increase light-extraction efficiency. After laser decomposition, laser scribing, and a lateral crystallographic wet etching process at the GaN/Al2O3 interface, stable crystallographic etching planes were formed as the GaN {1011¯} planes that included an angle with the top GaN (0001) plane measured at 58°. The GaN buffer layer acted as the sacrificial layer for the laser decomposition process and the lateral wet etching process with a 26 μm/min etching rate. The LED with the inverted pyramidal N-face GaN surface close to the GaN/Al2O3 interface has a larger light-scattering process than the conventional LED. The light-output power of the LED with the backside roughened surface had a 47% enhancement when measured in LED chip form.

InGaN light emitting diodes with a laser-treated tapered GaN structure.

InGaN light-emitting diode (LED) structures get an air-void structure and a tapered GaN structure at the GaN/sapphire interface through a laser decomposition process and a lateral wet etching process. The light output power of the treated LED structure had a 70% enhancement compared to a conventional LED structure at 20 mA. The intensities and peak wavelengths of the micro-photoluminescence spectra were varied periodically by aligning to the air-void (461.8nm) and the tapered GaN (459.5nm) structures. The slightly peak wavelength blueshift phenomenon of the EL and the PL spectra were caused by a partial compressed strain release at the GaN/sapphire interface when forming the tapered GaN structure. The relative internal quantum efficiency of the treated LED structure (70.3%) was slightly increased compared with a conventional LED (67.8%) caused by the reduction of the piezoelectric field in the InGaN active layer.

Chemical–Mechanical Lift-Off Process for InGaN Epitaxial Layers

An InGaN-based light-emitting diode (LED) structure was separated from a GaN/sapphire structure by inserting sacrificial Si-doped InGaN/GaN superlattice layers through a chemical–mechanical lift-off (CMLO) process. The CMLO process consisted of a band-gap-selective photoelectrochemical lateral wet etching process and a mechanical lift-off process. A lower elastic modulus and hardness of the lateral-etched LED structure were measured compared with the conventional LED structure, which indicated a weak mechanical property of the treated LED structure. The photoluminescence blue-shift phenomenon and the Raman redshift phenomenon indicated that the compressive strain from the bottom GaN/sapphire structure was released through the CMLO process.

InGaN Light-Emitting Diodes With the Inverted Cone-Shaped Pillar Structures

An InGaN-based light-emitting diode (LED) with an inverted cone-shaped pillar structure was fabricated through a plasma dry etching process and a photoelectrochemical (PEC) process. The undercut structure was fabricated through a bandgap-selective PEC etching process that occurred at the InGaN active layer. Then, the inverted cone-shaped pillar structure was formed through a bottom-up crystallographic etching process in a hot potassium hydroxide solution. The light-output power of the LED with an inverted cone-shaped pillar structure had a 42% enhancement compared with the standard LED without the pillar structure at a 20-mA operating current. A higher light intensity of the PEC-treated LED was observed around the mesa-edge region and the pillar structures as a result of a higher light-scattering process occurring at the inverted cone-shaped structure.

Green Light-Emitting Diodes with a Photoelectrochemically Treated Microhole-Array Pattern

Green InGaN-based light-emitting diodes (LEDs) with roughened microhole-array (MHA) structures were fabricated through a dry etching process and a photoelectrochemical (PEC) process. The PEC process consisted of a bandgap-selective lateral etching process at the InGaN active layer, an N-face bottom-up crystallographic etching process at the bottom p-type GaN:Mg layer, and a PEC oxidation process at the n-type GaN:Si surface. The light output power of the MHA-LED and the photoelectrochemically treated microhole-array light-emitting diode (PMHA-LED) had 7 and 65% enhancement, respectively, compared to a conventional LED at a 20 mA operation current.

Enhanced the Light Extraction Efficiency of an InGaN Light Emitting Diodes with an Embedded Rhombus-Like Air-Void Structure

InGaN light-emitting diodes (LED) were grown on a truncated-triangle-striped patterned sapphire substrate. After growing a GaN layer on the patterned-sapphire substrate, it was observed that a higher lateral growth process formed a V-shaped-striped air-void structure. After a bottom-up N-face wet etching process on a GaN layer, the stable crystallographic etching planes were formed as the GaN{1011} planes. Treated LED structures had 65% light enhancements and smaller divergent angles. A rhombus-like air-void structure formed at GaN/patterned-sapphire interface provided a high light extraction process and a wet etching channel for a chemical lift-off process application.

An AlN Sacrificial Buffer Layer Embedded into the InGaN Light Emitting Diodes for a Chemical Lateral Etching Process

High chemical lateral etching rate at AIN buffer/sacrificial layer embedded into GaN/patterned-sapphire substrate of InGaN-based light emitting diode (LED) was achieved. An air-void structure was observed at a truncated triangular patterned sapphire that provided an empty space to increase the lateral etching rate of the AIN sacrificial layer. A 30 μm wide lateral etched region was observed around the LED chip. After a chemical lateral wet-etching process on AlN sacrificial layer and a bottom-up N-face etching process on GaN epitaxial layer, the stable crystallographic etching planes were formed as GaN {1011} planes. The treated LED structure had a higher light-output power and a smaller divergent angle compared with conventional LED structure that had the potential application for the chemical lift-off process.