Abstract
The polarization fields and electro-optical response of PIN-diodes based on nearly lattice-matched InGaN/GaN and InAlN/GaN double heterostructure quantum wells grown on (0001) sapphire substrates by metalorganic vapor phase epitaxy were experimentally quantified. Dependent on the indium content and the applied voltage, an intense near ultra-violet emission was observed from GaN (with fundamental energy gap Eg = 3.4 eV) in the electroluminescence (EL) spectra of the InGaN/GaN and InAlN/GaN PIN-diodes. In addition, in the electroreflectance (ER) spectra of the GaN barrier structure of InAlN/GaN diodes, the three valence-split bands, Γ9, Γ7+, and Γ7−, could selectively be excited by varying the applied AC voltage, which opens new possibilities for the fine adjustment of UV emission components in deep well/shallow barrier DHS. The internal polarization field Epol = 5.4 ± 1.6 MV/cm extracted from the ER spectra of the In0.21Al0.79N/GaN DHS is in excellent agreement with the literature value of capacitance-voltage measurements (CVM) Epol = 5.1 ± 0.8 MV/cm. The strength and direction of the polarization field Epol = −2.3 ± 0.3 MV/cm of the (0001) In0.055Ga0.945N/GaN DHS determined, under flat-barrier conditions, from the Franz-Keldysh oscillations (FKOs) of the electro-optically modulated field are also in agreement with the CVM results Epol = −1.2 ± 0.4 MV/cm. The (absolute) field strength is accordingly significantly higher than the Epol strength quantified in published literature by FKOs on a semipolar ( 11 2 ¯ 2 ) oriented In0.12Ga0.88N quantum well.
Highlights
Engineering of efficient light emitting diodes (LEDs) and laser diodes (LDs) in the deep ultraviolet (UVC) range (100–280 nm) is a main goal of nanooptoelectronics and photonics [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]
The electric performance of the group-III nitride semiconductor PIN-diodes analyzed in the present work by electroreflectance (ER) and electroluminescence (EL) spectroscopy in view of performance relevant electro-optical field effects was initially approached by capacitance-voltage measurements (CVM) in [44]
A brief review of the CVM measurement principles applied in [44,45,46] on the PIN-diodes studied by ER and EL is given in the following, since it has delivered the built-in potential Vbi used to evaluate the polarization fields by ER
Summary
Engineering of efficient light emitting diodes (LEDs) and laser diodes (LDs) in the deep ultraviolet (UVC) range (100–280 nm) is a main goal of nanooptoelectronics and photonics [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]. A proven physical disinfection method in drinking water purification is the use of ultraviolet (UV) light with wavelengths of 200–300 nm to inactivate micro-organisms. The wavelength of the applied UV light depends on the implemented UV emitter. Low- and medium-pressure mercury lamps are used; in water purification applications, in discontinuously operated, decentralized, and mobile water systems, UV light emitting diodes have certain advantages compared to conventional UV emitters: they
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