We report indium incorporation properties on various nonpolar and semipolar free-standing GaN substrates. Electroluminescence characterization and x-ray diffraction (XRD) analysis indicate that the semipolar (202¯1¯) and (112¯2) planes have the highest indium incorporation rate among the studied planes. We also show that both indium composition and polarization-related electric fields impact the emission wavelength of the quantum wells (QWs). The different magnitudes and directions of the polarization-related electric fields for each orientation result in different potential profiles for the various semipolar and nonpolar QWs, leading to different emission wavelengths at a given indium composition.
We study the optical spectral properties for green semipolar (20 2 1) and (20 21) light-emitting diode (LED) with same indium compositions. Compared to (20 21) devices, the fabricated (20 2 1) micro-LED (0:005 mm 2 ) showed negligible blue shift and smaller full width at half maximum (FWHM) up to extremely high current densities (10,000 A/cm 2 ). Theoretical simulation indicates that the (20 2 1) InGaN quantum well (QW) has reduced polarization-related effects due to combined effects of electric field cancelling and Coulomb screening effect. In addition, the packaged device performance for small-area (0:144 mm 2 ) semipolar green (20 2 1) and (20 21) LEDs were also discussed. The green (20 2 1) LED showed smaller wavelength shift and narrower FWHM than green LEDs fabricated on other planes. #
Blue laser diodes (LDs) were fabricated on m-plane oriented GaN substrates by atmospheric-pressure metalorganic chemical vapor deposition. Typical threshold current for stimulated emission at a wavelength λ of 463 nm was 69 mA. Blueshift of the spontaneous emission peak with increasing injection current was examined in LDs fabricated on m- and c-plane GaN substrates. Blueshifts for the m-plane LD (λ=463 nm) and the c-plane LD (λ=454 nm) with an injection current density just below threshold were about 10 and 26 nm, respectively. These results confirm that the blueshift in quantum-wells fabricated on m-plane oriented substrates is smaller than on c-plane oriented substrates due to the absence of polarization-induced electric fields.
We investigate the influence of polarity on carrier transport in single-quantum-well and multiple-quantum-well (MQW) light-emitting diodes (LEDs) grown on the semipolar (20 21) and (2021) orientations of free-standing GaN. For semipolar MQW LEDs with the opposite polarity to conventional Ga-polar c-plane LEDs, the polarization-related electric field in the QWs results in an additional energy barrier for carriers to escape the QWs. We show that semipolar (2021) MQW LEDs with the same polarity to Ga-polar c-plane LEDs have a more uniform carrier distribution and lower forward voltage than (20 21) MQW LEDs.
We report on void defect formation in ð2021Þ semipolar InGaN quantum wells (QWs) emitting in the green spectral region. Fluorescence and transmission electron microscopy studies indicate that this type of defect is associated with voids with f10 11g, f10 10g, and f000 1g side facets in the QW region. Systematic growth studies show that this defect can be effectively suppressed by reducing the growth rate for the active region. Green light-emitting diodes (LEDs) with reduced active region growth rate showed enhanced power and wavelength performance. The improved LED performance is attributed to the absence of void defects in the active region.
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