In this research nanoporous structures on p-type GaN:Mg and n-type GaN:Si surfaces were fabricated through a photoelectrochemical (PEC) oxidation and an oxide-removing process. The photoluminescence (PL) intensities of GaN and InGaN∕GaN multi-quantum-well (MQW) structures were enhanced by forming this nanoporous structure to increase light extraction efficiency. The PL emission peaks of an MQW active layer have a blueshift phenomenon from 465.5nm (standard) to 456.0nm (nanoporous) measured at 300K which was caused by partially releasing the compressive strain from the top GaN:Mg layers. The internal quantum efficiency could be increased by a partial strain release that induces a lower piezoelectric field in the active layer. The thermal activation energy of a nanoporous structure (85meV) is higher than the standard one (33meV) from a temperature dependent PL measurement. The internal quantum efficiency and light extraction efficiency of an InGaN∕GaN MQW active layer are significantly enhanced by this nanoporous GaN:Mg surface, and this PEC treated nanoporous structure is suitable for high-power lighting applications.

InGaN light emitting diodes (LED) structure with an embedded 1/4λ-stack nanoporous-GaN/undoped-GaN distributed Bragg reflectors (DBR) structure have been demonstrated. Si-heavily doped GaN epitaxial layers (n⁺-GaN) in the 12-period n⁺-GaN/u-GaN stack structure are transformed into low refractive index nanoporous GaN structure through the doping-selective electrochemical wet etching process. The central wavelength of the nanoporous DBR structure was located at 442.3 nm with a 57 nm linewidth and a 97.1% peak reflectivity. The effective cavity length (6.0λ), the effective penetration depth (278 nm) in the nanoporous DBR structure and InGaN active layer matching to Fabry-Pérot mode order 12 were observed in the far-field photoluminescence radiative spectra. High electroluminescence emission intensity and line-width narrowing effect were measured in the DBR-LED compared with the non-treated LED structure. Non-linear emission intensity and line-width reducing effect, from 11.8 nm to 0.73 nm, were observed by increasing the laser excited power. Resonant cavity effect was observed in the InGaN LED with bottom nanoporous-DBR and top GaN/air interface.

In this work, we used the chemical vapor transport (CVT) method to grow PbI₂ crystals using iodine as a self-transporting agent. The crystals’ structure, composition, and uniformity were confirmed by X-ray diffraction (XRD) and electron probe microanalysis (EPMA) measurements. We investigated the band gap energy using absorption spectroscopy measurements. Furthermore, we explored the temperature dependence of the band gap energy, which shifts from 2.346 eV at 300 K to 2.487 eV at 20 K, and extracted the temperature coefficients. A prototype photodetector with a lateral metal–semiconductor–metal (MSM) configuration was fabricated to evaluate its photoelectric properties using a photoconductivity spectrum (PC) and persistent photoconductivity (PPC) experiments. The resonance-like PC peak indicates the excitonic transition in absorption. The photoresponse I_Light/I_Dark-1 is up to 200%.

InGaN based resonant-cavity light-emitting diode (RC-LED) structures with an embedded porous-GaN/n-GaN distributed Bragg reflector (DBR) and a top dielectric Ta₂O₅/SiO₂ DBR were demonstrated. GaN:Si epitaxial layers with high Si-doping concentration (n⁺-GaN:Si) in the 20-period n⁺-GaN/n-GaN stacked structure were transformed into a porous-GaN/n-GaN DBR structure through the doping-selective electrochemical wet etching process. The central wavelength and reflectivity were measured to be 434.3 nm and 98.5% for the porous DBR and to be 421.3 nm and 98.1% for the dielectric DBR. The effective 1λ cavity length at 432nm in the InGaN resonant-cavity consisted of a 30 nm-thick Ta₂O₅ spacer and a 148 nm-thick InGaN active layer that was analyzed from the angle-resolved photoluminescence (PL) spectra. In the optical pumping PL spectra, non-linear emission intensity and linewidths reducing effect, from 6.5 nm to 0.7 nm, were observed by varying the laser pumping power. Directional emission pattern and narrow linewidth were observed in the InGaN active layer with bottom porous DBR, top dielectric DBR, and the optimum spacer layer to match the short cavity structure.

The <mml:math display="inline"><mml:mrow><mml:mi>InGaN</mml:mi></mml:mrow></mml:math>InGaN -based light-emitting diode (LED) with an inclined undercut structure is fabricated through the photoelectrochemical two-step process to increase light extraction efficiency. In the first step the sidewall-undercut structure at the p-type and n-type <mml:math display="inline"><mml:mrow><mml:mi>GaN</mml:mi></mml:mrow></mml:math>GaN interface is created by selective wet oxidation on an n-type <mml:math display="inline"><mml:mrow><mml:mi>GaN</mml:mi></mml:mrow></mml:math>GaN surface in pure <mml:math display="inline"><mml:mrow><mml:msub><mml:mi mathvariant="normal">H</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mi mathvariant="normal">O</mml:mi></mml:mrow></mml:math>H2O solution. In the second step an inclined undercut structure through a crystallographic wet-etching process is formed by immersion in hot <mml:math display="inline"><mml:mrow><mml:mi>KOH</mml:mi></mml:mrow></mml:math>KOH solution. This crystallographic wet-etching process can remove the <mml:math display="inline"><mml:mrow><mml:msub><mml:mi>Ga</mml:mi><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>Ga2O3 layer and form a <mml:math display="inline"><mml:mrow><mml:mo>{</mml:mo><mml:mn>10</mml:mn><mml:mover accent="true"><mml:mrow><mml:mn>11</mml:mn></mml:mrow><mml:mo stretchy="true">¯</mml:mo></mml:mover><mml:mo>}</mml:mo></mml:mrow></mml:math>{1011¯} p-type <mml:math display="inline"><mml:mrow><mml:mi>GaN</mml:mi></mml:mrow></mml:math>GaN stable plane, <mml:math display="inline"><mml:mrow><mml:mo>{</mml:mo><mml:mn>10</mml:mn><mml:mover accent="true"><mml:mrow><mml:mn>1</mml:mn></mml:mrow><mml:mo stretchy="false">¯</mml:mo></mml:mover><mml:mn>0</mml:mn><mml:mo>}</mml:mo></mml:mrow></mml:math>{101¯0} n-type <mml:math display="inline"><mml:mrow><mml:mi>GaN</mml:mi></mml:mrow></mml:math>GaN stable plane on the mesa sidewall. This inclined p-type <mml:math display="inline"><mml:mrow><mml:mi>GaN</mml:mi></mml:mrow></mml:math>GaN plane of LED structure can provide the higher overlap of incident light beam core and extraction core overlap on the mesa sidewall, and the total light output power of the treated LED is 2.10 times higher than the standard LED. Consequently, this inclined undercut LED structure is suitable for high-efficiency nitride-based LED application.