RESUMEN
High channel current of the high electron mobility transistors (HEMTs) and high relative responsivity of the photodetectors (PDs) were demonstrated in the AlGaN/AlN/GaN channel-stacking epitaxial structures. The interference properties of the X-ray curves indicated high-quality interfaces of the conductive channels. The AlGaN/AlN/GaN interfaces were observed clearly in the transmission electron microscope micrograph. The saturation I ds currents of the HEMT structures were increased by adding a number of channels. The conductive properties of the channel-stacking structures corresponded to the peaks of the transconductance (g m) spectra in the HEMT structures. The depletion-mode one- and two-channel HEMT structures can be operated at the cutoff region by increasing the reverse V gs bias voltages. Higher I ds current in the active state and lower current in the cutoff state were observed in the two-channel HEMT structure compared with one- and three-channel HEMT structures. For the channel-stacking metal-semiconductor-metal photodetector structures, the peak responsivity was observed at almost 300 nm incident monochromic light, which was increased by adding a number of channel layers. The channel current of the HEMT devices and the photocurrent in the PD devices were increased by adding a number of two-dimensional electron gas (2DEG) channels. By using a flat gate metal layer, the two-channel AlGaN/AlN/GaN HEMT structures exhibited a high I ds current, a low cutoff current, and a high peak g m value and have the potential for GaN-based power devices, fast portable chargers, and ultraviolet PD applications.
RESUMEN
Ultraviolet-C AlGaN resonant-cavity light-emitting diodes with top and bottom pipe-AlGaN-distributed Bragg reflectors (DBRs) have been demonstrated. For the top/bottom DBR structures, 20 pairs of n+-AlGaN:Si/n-AlGaN:Si stack structures were transformed into the pipe-AlGaN:Si/n-AlGaN:Si DBRs through a doping-selective electrochemical wet etching process. The reflectivity of the pipe-AlGaN DBR structure was measured as 90% at 276.7 nm with a 20.9 nm flat stopband width. The anisotropic optical properties of the pipe-AlGaN DBR structure had been analyzed through the polarization-dependent reflectance spectra. For temperature-dependent reflectance spectra, the central wavelengths were slightly redshifted from 275 nm (100 K) to 281 nm (600 K) due to thermal expansion, refractive index increase, and partial strain release phenomena in the pipe-DBR structure. High photoluminescence emission intensity and line-width reducing phenomena were observed at 10 K in the UVC-LED with the resonant-cavity structure, which has potential for high-efficiency UV-C light source applications.
RESUMEN
We report here a simple and robust process to convert periodic Si-doped GaN/undoped-GaN epitaxial layers into a porous-GaN/u-GaN distributed Bragg reflector (DBR) structure and demonstrate its material properties in a high-reflectance epitaxial reflector. Directional pipe-GaN layers with anisotropic optical properties were formed from n+-GaN : Si layers in a stacked structure through a lateral and doping-selective electrochemical etching process. Central wavelengths of the polarized reflectance spectra were measured to be 473 nm and 457 nm for the pipe-GaN reflector when the direction of the linear polarizer was along and perpendicular to the pipe-GaN structure. The DBR reflector with directional pipe-GaN layers has the potential for a high efficiency polarized light source and vertical cavity surface emitting laser applications.
RESUMEN
A GaN/AlGaN ultraviolet light emitting diode (UV-LED) structure with a porous AlGaN reflector structure has been demonstrated. Inside the UV-LED, the n+-AlGaN/undoped-AlGaN stack structure was transformed into a porous-AlGaN/undoped-AlGaN stack structure through a doping-selective electrochemical etching process. The reflectivity of the porous AlGaN reflector was 93% at 374 nm with a stop-bandwidth of 35 nm. In an angle-dependent reflectance measurement, the central wavelength of the porous AlGaN reflector had blueshift phenomenon by increasing light-incident angle from 10° to 50°. A cut-off wavelength was observed at 349 nm due to the material absorption of the porous-AlGaN/u-AlGaN stack structure. In the treated UV-LED structure, the photoluminescence emission wavelength was measured at 362 nm with a 106° divergent angle covered by the porous-AlGaN reflector. The light output power of the treated UV-LED structure was higher than that of the non-treated UV-LED structure due to the high light reflectance on the embedded porous AlGaN reflector.