Selman Mutlu | Anadolu University (original) (raw)

Papers by Selman Mutlu

Materials Science in Semiconductor Processing

Journal of Alloys and Compounds

Abstract In this work, an InGaN/GaN multiple quantum well based Top-Hat Hot-Electron Light Emissi... more Abstract 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.

physica status solidi (RRL) – Rapid Research Letters

Semiconductor Science and Technology, 2018

We present the results of longitudinal carrier transport under a high electrical field in n- and ... more We present the results of longitudinal carrier transport under a high electrical field in n- and p-type modulation-doped Ga0.68In0.32NyAs1−y/GaAs (y = 0.009, 0.017) quantum well (QW) structures. Nitrogen composition-dependent drift velocities of electrons are observed to be saturated at and at 77 K for the samples with y = 0.009 and y = 0.017, respectively, while the drift velocities of holes do not saturate but slightly increase at the applied electric field in the range of interest. The hole drift velocity is observed to be higher than the electron drift velocity. The electron mobility exhibits an almost temperature-independent characteristic. On the other hand, the hole mobility exhibits a conventional temperature dependence of modulation-doped QW structures. As the temperature increases, the drift velocity of the electrons exhibits an almost an temperature-insensitive characteristic, but, on the other hand, for holes, drift velocity decreases approximately from 107–106 cm s−1. It is observed that the drift velocities of electrons and holes are N-dependent and suppressed at higher electric fields. Furthermore, experimental results show that there is no evidence of negative differential velocity (NDV) behaviour for both n- and p-type samples. To explore the observed electron and hole drift velocity characteristic at high electric fields, we use a simple theoretical model for carrier transport, which takes into account the effect of non-drifting hot phonons. The mobility mapping technique (comparison method) is used to extract hot hole temperature in order to employ it in the non-drifted phonon distribution and to obtain the drift velocity–electric field curves. Then hot electron temperatures are obtained from the drift velocity–electric field curves as a fit parameter using non-drifted hot phonon dynamics. The analytical model is well-matched to the experimental –E curves, indicating that carrier-hot phonon scattering is the main reason for suppressing the NDV mechanism in GaInNAs/GaAs QW structures with a carrier density higher than 1017 cm−3.

Superlattices and Microstructures, 2017

Abstract We report room temperature operation of light emitters based on Al 0.08 Ga 0.92 As Gunn ... more Abstract We report room temperature operation of light emitters based on Al 0.08 Ga 0.92 As Gunn devices fabricated in a simple bar geometry with wedged-shaped electrodes. High-speed I-V measurements reveal that, at the threshold of negative differential resistance region at around 3.8 kV/cm, current instabilities, i.e., Gunn oscillations, are created with a 3.8 ns period. Both edge and surface light emission are observed when the device is biased at an electric field of onset of the negative differential resistance (NDR) region at around 3.8 kV/cm and the intensity of the light exponentially increases at applied fields just above NDR threshold likewise in a conventional laser. The origin of the light emission, which has peak wavelength is around 816 nm corresponds to the band-gap energy of Al 0.08 Ga 0.92 As, is recombination of electrons and holes generated by impact ionisation process in travelling space charge domains, i.e. , Gunn domains. We demonstrate that, with increasing applied field, the amplitude of Gunn domains increases which is a result of the enhanced generation of electrons and holes via impact ionisation. The intensity of the emitted light is observed to be dependent on applied electric field. At low electric fields, light intensity increases linearly then, when applied electric field reaches the onset of NDR region, increases exponentially. Besides, as applied field is increased, full width at half maximum (FWHM) of emitted light decreases to 56.5 nm from 62 nm, evolving into higher selective emission line in wavelength. The light emission from the device is determined to be independent of the polarity of the applied voltage. A comparison of surface emission and edge emission characteristics of the waveguided device are different from each other. Edge emission has higher electroluminescence intensity and better spectral purity than surface emission with well-defined longitudinal modes of Fabry-Perot cavity, which indicates that, in such a device, lasing action arises from the recombination of excess carriers generated via impact ionisation in travelling Gunn domains. Besides, the edge emission peak of waveguided Al 0.08 Ga 0.92 As Gunn device at 4.1 kV/cm is split into two peaks with FWHM of 8 and 6 nm as well as neighbouring sharper minor peaks due to stimulated emission dominates by building-up photons in the cavity. Our results reveal that the proposed Gunn device can be a promising alternative to conventional diode lasers with its simpler design, only one type doped active region and voltage polarity-independent operation, but the duty cycle has to be chosen small enough to make the device operate at room temperature.

Journal of Alloys and Compounds, 2017

Effect of thermal annealing and nitrogen composition on quantum transport in GaInNAs alloy based ... more Effect of thermal annealing and nitrogen composition on quantum transport in GaInNAs alloy based modulation doped quantum well structures,

Journal of Electronic Materials, 2015

Molecular beam epitaxy-grown In x Ga 1Àx N/GaN samples with indium fraction x ranging between 0.4... more Molecular beam epitaxy-grown In x Ga 1Àx N/GaN samples with indium fraction x ranging between 0.44 and 0.784 were studied by pulsed current-voltage (I-V) measurements at 1.7 K. The drift velocity, electron mobility, and electric-field-dependent power loss per electron were determined from analysis of the data. The drift velocity increased linearly while the electron mobility remained constant with increasing electric field. Power balance equations were used to obtain the power loss per electron as a function of the applied electric field in the range of 0 kV cm À1 to 230 kV cm À1. The results showed that the power loss per electron increased in the x range of 0.44 to 0.66, then slowly decreased in the x range of 0.66 to 0.784. The results obtained for the dependence of the power loss on the electron temperature are compared with current theoretical models for the power loss in two-dimensional (2D) semiconductors, which include both piezoelectric and deformation potential scattering. For all samples, the energy relaxation of electrons is dominated by acoustic phonon emission via piezoelectric interaction.

Journal of Physics D: Applied Physics, 2015

ABSTRACT

Materials Science and Engineering: B, 2012

ABSTRACT The photoconductivity of p-i-n GaInNAs/GaAs multiple quantum well (MQW) mesa structures ... more ABSTRACT The photoconductivity of p-i-n GaInNAs/GaAs multiple quantum well (MQW) mesa structures is investigated. When illuminated with photons at energy greater than the GaAs bandgap, a number of oscillations are observed in the current–voltage I–V characteristics. The amplitude and position of the oscillations is shown to depend upon the temperature, as well as upon the exciting wavelength and intensity. Due to the absence of the oscillations in the dark I–V and at temperatures above T = 200 K, we explain them in terms of photogenerated electrons escaping from quantum wells via tunnelling or thermionic emission. Magnetic fields up to B = 11 T were applied parallel to the planes of the QWs. A small voltage shift in the position of the oscillations was observed, proportional to the magnetic field intensity and dependent upon the temperature. Calculation of the Landau level energy separation (16 meV) agrees with the observed experimental data. Magneto-tunnelling spectroscopy probes in detail the nature of band- or impurity-like states responsible for resonances in first and second subbands, observing the I–V plot in dark condition and under illumination. The field-dependence of the amplitude of the oscillation peaks in I–V has the characteristic form of a quantum mechanical admixing effect. This enhancement is also probably due to the hole recombination with majority electrons tunnelling in the N-related states of the quantum wells.

Superlattices and Microstructures, 2012

The two-dimensional (2D) electron energy relaxation in Al 0.25 Ga 0.75 N/AlN/GaN heterostructures... more The two-dimensional (2D) electron energy relaxation in Al 0.25 Ga 0.75 N/AlN/GaN heterostructures was investigated experimentally by using two experimental techniques; Shubnikov-de Haas (SdH) effect and classical Hall Effect. The electron temperature (T e) of hot electrons was obtained from the lattice temperature (T L) and the applied electric field dependencies of the amplitude of SdH oscillations and Hall mobility. The experimental results for the electron temperature dependence of power loss are also compared with the current theoretical models for power loss in 2D semiconductors. The power loss that was determined from the SdH measurements indicates that the energy relaxation of electrons is due to acoustic phonon emission via unscreened piezoelectric interaction. In addition, the power loss from the electrons obtained from Hall mobility for electron temperatures in the range T e > 100 K is associated with optical phonon emission. The temperature dependent energy relaxation time in Al 0.25 Ga 0.75 N/AlN/GaN heterostructures that was determined from the power loss data indicates that hot electrons relax spontaneously with MHz to THz emission with increasing temperatures.