•The scattering mechanisms limiting mobility were investigated in quaternary samples.•Influences of thickness and alloy composition of the quaternary layer on mobility.•Determining interface-related ...parameters.
The electron mobility limited by different scattering mechanisms in the quaternary AlInGaN alloy grown on a GaN layer is investigated with the classical Hall measurement, which is performed at a temperature range of 12 and 350 K and a magnetic field of B = 0.51 T. The effect of the thickness and alloy composition of the quaternary AlInGaN layer on the mobility is also determined. The experimentally determined temperature-dependent Hall mobility was compared with mobility calculated by using Matthiessen's rule. The main scattering mechanisms, including acoustic phonon scattering (piezoelectric and deformation potential), polar optical phonon scattering, alloy disorder scattering, interface roughness scattering, ionized impurity scattering, dislocation scattering, background impurity scattering, were used in the calculations for all temperatures. The results show that the dominant scattering mechanisms, depending on the investigated sample, are the interface roughness scattering and alloy disorder scattering at almost all temperatures. At a low-temperature, mobility is limited by ionized impurity scattering. High-temperature mobility is limited by polar optical phonon scattering. Furthermore, our results suggest that the thickness and alloy composition of the quaternary AlInGaN layer should be optimized for better transport properties.
The photoluminescence (PL) properties of InGaN/GaN multiple quantum wells (MQWs) samples with a different quantum well number (two, three, and four) grown by molecular beam epitaxy have been studied ...in the temperature range between 3 and 300 K. The redshift-blueshift-redshift in the PL peak energy of InGaN well, which is known that as S-shaped behavior, is observed with increasing temperature in the investigated samples. S-shaped behavior is associated with carrier localization states and inhomogeneity in InGaN/GaN MQWs samples. This behavior is explained with the theoretical band tail model. The parameters showing the effect of carrier localization degree are determined and discussed in detail. Furthermore, it is presented the activation energy of charge carriers by using InGaN related-normalized PL peak intensity as a function of the reverse of temperature and Arrhenius function for all samples. The highest PL intensity is obtained in sample B with 3-QWs. Determining carrier localization effect and activation energy plays a vital role in luminescence efficiency and quality of InGaN/GaN MQWs devices.
•TH-HELLISH device is based on the InGaN/GaN multi QW structure.•The emission wavelength and light intensity are independent from the polarity.•Potential usage as XOR optical logic gate.
In this ...work, an InGaN/GaN multiple quantum well based Top-Hat Hot-Electron Light Emission and Lasing in a Semiconductor Heterostructure (Top-Hat HELLISH) is investigated. A heterojunction structure is designed based on an active InGaN quantum well placed in the n-type GaN region sandwiched by the n- and p-type GaN layers. The four quantum well structure of an InGaN/GaN heterojunction where the Indium ratio is 0.16 has been grown via Metal-Organic Chemical Vapor Deposition. In order to create an anisotropic potential distribution of the heterojunction, it is aimed to fabricate TH-HELLISH-GaN device in Top-Hat HELLISH (THH) geometry for four contacts with separate n- and p-channels. High-speed I-V measurements of the device reveal an Ohmic characteristic at both polarities of the applied voltage. Integrated EL measurements reveal the threshold of the applied electric field at around 0.25 kV/cm. The emission wavelength of the device is around 440 ± 1 nm at room temperature.
Optical scintillating bers lose their transparencies when exposed to radiation. Nearly all studies of radiation damage to optical bers so far only characterize this darkening with a single period of ...irradiation. Following the irradiation, bers undergo room temperature annealing, and regain some of their transparencies. We tested the irradiation-recovery characteristics of scintillating fibers in four consecutive cycles. In addition, three optical scintillating bers were irradiated at 22 Gy per minute for over 15 hours, and their transmittance were measured each minute by pulsing a light source through the bers. Here, we report on the in-situ characterization of the transmittance vs radiation exposure, allowing future applications to better predict the lifetime of the scintillating bers.
PEN and PET (polyethylene naphthalate and teraphthalate) are common plastics used for drink bottles and plastic food containers. They are also good scintillators. Their ubiquity has made them of ...interest for high energy physics applications, as generally plastic scintillators can be very expensive. However, detailed studies on the performance of the scintillators has not yet been performed.
At various tests, we measured the light yield and timing properties of PEN and PET with Fermilab and CERN test beams. We also irradiated several samples to varying gamma doses and investigated their recovery mechanisms. Here we report on the measurements performed over the past few years in order to characterize the scintillation properties of PEN and PET and discuss possible future implementations.
The electron effective masses in n-type modulation doped Ga
0.7
In
0.3
N
y
As
1−
y
/GaAs quantum wells with nitrogen mole fractions of
y
= 0.004 and 0.010 were investigated experimentally. Two ...experimental techniques: magnetic field dependent photoluminescence measurements and phonon-plasmon coupled-mode line-shape analysis of vibrational spectroscopy measurements, were employed in the investigations. In the first technique, the effective masses of the electrons have been determined from the diamagnetic energy shift dependencies up to 11 T. The vibrational properties of the samples were studied using Raman scattering spectroscopy at room temperature. The effective masses obtained from both two techniques are in good agreement with the current results in the literature.
The effects of surface passivation effect on electron mobility and crystal structure in Al0.3Ga0.7N/AlN/GaN heterostructures are investigated by classical Hall effect measurements and an X‐ray ...diffraction method. Al0.3Ga0.7N/AlN/GaN heterostructures with different doping and layer structures were grown by molecular beam epitaxy with or without growing an in situ SiN passivation layer. The classical Hall effect measurements were carried out as a function of temperature in the range between T = 1.82 K and 270 K at a fixed magnetic field in dark conditions. The effect of doping of the barrier layer and replacing an AlN inter‐layer between the AlGaN barrier and the GaN layer, where the two‐dimensional electron gas is populated, on mobility and sheet carrier concentration were also determined.
In this work, the functioning of the Top-Hat Hot-Electron Light Emission and Lasing in a Semiconductor Heterostructure (TH-HELLISH) structure, which is based on InGaN/GaN multiple quantum wells, is ...investigated to employ it as an optical amplifier and wavelength converter. The heterojunction structure is formed by placing four InGaN quantum wells in the n-type GaN region between the n- and p-type GaN layers. The device with a TH-HELLISH structure was grown on a sapphire (Al2O3) substrate by Metal-Organic Chemical Vapor Deposition (MOCVD) with an indium ratio of 0.16. The TH-HELLISH device was fabricated in Top-Hat HELLISH (THH) geometry with four independent n- and p-channels contacts to create a non-isotropic potential distribution in the heterojunction. The electro-photoluminescence (E-PL) technique was used to obtain light amplification and the converted wavelength. A 370 nm excitation light is absorbed by the TH-HELLISH device, subsequently leading to the emission at 440 ± 1 nm, which fulfills the role of a wavelength converter. It was also observed that TH-HELLISH operates as an optical amplifier with a 1.6-times increase in emission at 370 nm excitation. When the device is illuminated with a wavelength of 370 nm, it is monitored that the threshold electric field decreased from 0.25 kV/cm to 0.18 kV/cm, accompanied by a corresponding decrease in the threshold voltage from 12.5 V to 9.0 V. In addition, the TH-HELLISH device is found to be operated independently of the polarity of the applied voltage, and the absorption and emission regions of the device can be switched by changing the polarity of the applied voltage, therefore behaving as a bi-directional wavelength converter and optical amplifier.
•TH-HELLISH device is investigated to employ it as an optical amplifier and wavelength converter at room temperature.•A 370 nm excitation light is absorbed by the TH-HELLISH device, subsequently leading to the modulation of 440 ± 1 nm light.•It was also observed that TH-HELLISH operates as an optical amplifier with a 1.6-times increase in emission at 370 nm excitation.•It is observed that the threshold electric field decreased when the device is illuminated with a wavelength of 370 nm.
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