The influence of carrier localization on photoluminescence efficiency droop and stimulated emission is studied in AlGaN multiple quantum wells with different strength of carrier localization. We ...observe that carrier delocalization at low temperatures predominantly enhances the nonradiative recombination and causes the droop, while the main effect of the delocalization at elevated temperatures is enhancement of PL efficiency due to increasing contribution of bimolecular recombination of free carriers. When the carrier thermal energy exceeds the dispersion of the potential fluctuations causing the carrier localization, the droop is caused by stimulated carrier recombination.
The results on design, fabrication, and characterization of a hot-electron bolometer (HEB) based on the low-mobility two-dimensional electron gas (2DEG) in a AlGaN/GaN heterostructures show that our ...HEBs have high coupling to incident THz radiation due to the Drude absorption. Significant heating by THz radiation is realized due to the small value of the electron heat capacity. A low contact resistance achieved in our devices ensures that the THz radiation couples primarily to the 2DEG. Due to the small electron momentum relaxation time, the real part of the 2DEG sensor impedance is ~50–100 Ω, which provides a good impedance match between the sensor and antenna. Currently the room temperature responsivity of our devices reaches ~ 0.04 A/W at 2.55 THz along with a noise equivalent power ~ 5 nW/Hz1/2 at room temperature.
Nonradiative recombination rate and diffusivity of nonequilibrium carriers were modified by intense laser pulses in AlGaN epilayers with Al content ranging from 16 to 71%. The epilayers were examined ...before and after the photomodification using light-induced transient grating and photoluminescence spectroscopy techniques. The photomodification resulted in (i) enhancement of the nonradiative recombination rate and (ii) large changes of the diffusion coefficient of the nonequilibrium carriers, without imposing any macroscopic structural damage to the epilayers. The photomodification effect on the recombination rate was stronger in the layers with higher Al content indicating the involvement of the Al atoms in this process. The carrier diffusivity exhibited a rapid initial increase as a consequence of the photomodification followed by a slow decline, as the photomodification duration was increased. The enhancement of the diffusion coefficient of up to 2.4 times was accompanied by 13% decrease in the carrier lifetime.
•AlGaN layers were photomodified without surface damage by intense laser pulses.•During modification, high-density photoexcited carriers activated new defects.•These defects permanently reduced free carrier nonradiative lifetime and IQE.•Photomodification susceptibility increases with Al content in the AlGaN layers.•A short laser photomodification also permanently enhanced the carrier diffusivity.
Deep-Ultraviolet Light-Emitting Diodes Shur, M.S.; Gaska, R.
IEEE transactions on electron devices,
2010-Jan., 2010-01-00, 20100101, Letnik:
57, Številka:
1
Journal Article
Recenzirano
Compact solid-state deep-ultraviolet (DUV) light-emitting diodes (LEDs) go far beyond replacing conventional DUV sources such as mercury lamps. DUV LEDs enable new applications for air, water, and ...surface sterilization and decontamination, bioagent detection and identification, UV curing, and biomedical and analytical instrumentation. We review materials growth, device physics, design, fabrication, and performance of DUV LEDs with wavelength ranging from 210 to 365 nm, describe prototype systems for water purification and sterilization, and discuss other emerging applications and systems using DUV LEDs.
The response of GaN/sapphire SAW delay line to the focused ultraviolet (UV) illumination was investigated at the SAW frequency 306 MHz and optical wavelength 375 nm. The UV irradiation of an ...interdigital transducer (IDT) led to 4 to 5 times larger phase change of transmitted signal than the irradiation of the surface acoustic wave (SAW) propagation path between the IDTs at the same UV light spot size of 2.4 mm. The UV-induced phase change has been attributed to the variation in IDT impedance due to photo-capacitive effect. Simulation of the SAW sensor phase response on the basis of this model is in good agreement with experimental results.
A comparative study of epitaxy of AlN, GaN and their alloys, grown on
c-axis and off-axis substrates of single-crystal aluminum nitride has been carried out. Growth on off-axis (>30°) substrates ...appears to result in rough surfaces and the absence of two-dimensional electron gas (2DEG). However, smooth morphologies were demonstrated for both homoepitaxial and heteroepitaxial growth on on-axis (<2°) substrates. On one of these oriented substrates a 2DEG, with a mobility of 1000
cm
2/V
s and a sheet density of 8.5×10
12
cm
−2 at room temperature, was also demonstrated for the first time.
The novel HFET design using perforated channel region under the gate reduces drain and source parasitic resistances due to the current spreading effect in the source-gate and gate-drain regions. ...Demonstrated results for AlGaN/GaN HFET show that the RONCG time constant reduces around two times using simple and robust perforated channel device processing. These results are especially important for new generations of power switching transistors.
The photoluminescence droop effect, i.e., the decrease in emission efficiency with increasing excitation intensity, is observed and studied in GaN epilayers with different carrier lifetimes. ...Spontaneous and stimulated emissions have been studied in the front-face and edge emission configurations. The onset of stimulated recombination occurs simultaneously with the droop onset in the front-face configuration and might be considered as an origin of the droop effect in GaN epilayers.
PDF
