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III Nitrides for Gas Sensing Applications
Published in Ankur Gupta, Mahesh Kumar, Rajeev Kumar Singh, Shantanu Bhattacharya, Gas Sensors, 2023
This is a FET device that incorporates a junction between two materials with different band gaps (i.e., a heterojunction) as the channel instead of a doped region which is used in the standard metal-oxide-semiconductor FET (MOSFET). The origin of HEMT dates back to 1977 with the development of GaAs-based MOSFET to attain superior high-speed performance over Si-based counterparts [11]. However, the absence of electrons at the interface between the oxide and GaAs due to high density of surface states in oxide led to search for alternate structure. A breakthrough was obtained while studying modulation-doped heterojunction superlattices of a thin layer of n-type AlGaAs and undoped GaAs [12]. Electrons supplied by donors in AlGaAs move into GaAs and achieve high mobility. As two materials of different band gaps are brought in contact, there appears a discontinuity in the band diagram and a two-dimensional layer is formed which is filled with electrons from the parent AlGaAs layer into GaAs. This electron accumulation channel in GaAs is termed as two-dimensional electron gas (2DEG). Using a field effect from Schottky gate placed on AlGaAs to modulate the electrons at this interface forms the basis of devices known as modulation doped field effect transistors (MODFET) or high electron mobility transistors (HEMT) [13]. These transistors switch ON or OFF in slightly more than 10 ps. It functions both as a digital switch as well as an analog amplifier [14]. A typical HEMT architecture with GaN/AlGaN and a typical energy band diagram for a generic HEMT is shown in Figure 8.3.
Field-Effect Transistors
Published in Nassir H. Sabah, Electronics, 2017
An improvement over the simple MESFET is the modulation-doped field-effect transistor (MODFET), also known as high-electron-mobility transistor (HEMT), illustrated in longitudinal section in Figure 5.7.3. A layer of heavily doped n-type AlGaAs is formed underneath the gate, which together with the gate, source, and drain, form a MESFET structure. However, a very thin layer of undoped AlGaAs separates the heavily doped layer from the GaAs substrate. AlGaAs has a wider bandgap than GaAs. Hence, although the n+-AlGaAs provides the conduction electrons, these electrons preferentially move to the GaAs, where their energies in the conduction band are lower because of the narrower energy gap. What is referred to as a two-dimensional (2-D)electron gas is formed in the GaAs boundary region, the current due to these electrons being controlled by the gate voltage. Electron mobility is considerably higher in the undoped GaAs, because electrons are not scattered by any impurity atoms (Section 2.6, Chapter 2). The purpose of the thin undoped AlGaAs layer is to enhance the isolation between the donor impurities of the n+-AlGaAs layer and the 2-D electron gas.
Silicon Nanostructures for Optical Communications
Published in Anwar Sohail, Raja M Yasin Anwar Akhtar, Raja Qazi Salahuddin, Ilyas Mohammad, Nanotechnology for Telecommunications, 2017
Adam A. Filios, Yeong S. Ryu, Kamal Shahrabi, Raphael Tsu
For example, modern telecommunication lasers utilize superlattices of InGaAsP/InP or GaAs/AlGaAs in the active region resulting in much improved line width characteristics. Blue light-emitting gallium nitride lasers that were discovered in the mid-1990s use superlattice construction. Vertical cavity surface emitting lasers (VCSELs), which are considered to be an emerging technology offering many benefits in terms of cost and performance for metropolitan area optical networks, consist of superlattices and quantum wells typically grown by MBE. High mobility transistors based on GaAs/AlGaAs superlattices are been considered for high-speed electronics. In addition to the superlattices based on the III–V materials system, strain layer superlattices of Si/SiGe are being considered for use in high-speed electronic devices.
Controllable nonlinear effects in a hybrid optomechanical semiconductor microcavity containing a quantum dot and Kerr medium
Published in Journal of Modern Optics, 2019
Sonam Mahajan, Aranya B. Bhattacherjee
The two optically coupled cavities are fabricated with the help of a set of DBR. Light confinement is achieved by the combined action of DBR along the x-direction and air guiding dielectric which provides confinement in the y−z plane (55). DBR mirror consists of quarter-wavelength thick high and low refractive index layers. The reflectance of DBR is proportional to the number of pairs and the difference between high and low index pairs (56). The first and the last layers are AlGaAs. This enhances the coupling of light in/out of the structure since the refractive index of AlGaAs lies between those of GaAs and air (56). GaAs-based mechanical resonators are fabricated by utilizing standard micromachining techniques with selective etching (57,58). A Kerr nonlinear substrate can be deposited on the GaAs cavity according to known experimental technique (59).
Effects of hydrostatic pressure and temperature on the nonlinear optical properties of GaAs/GaAlAs zigzag quantum well
Published in Philosophical Magazine, 2022
A. Turker Tuzemen, H. Dakhlaoui, F. Ungan
In addition to the studies mentioned above, the other works included triangular forms such as QWs, wires and dots are as follows: Chen et al. [36,37] have analysed theoretically the nonlinear optical rectification and the second harmonic generation (SHG) for GaAs/AlxGa1−xAs double triangular QWs, respectively. Yang et al. [38] have investigated the optical characteristics of InGaN/GaN triangular QWs in their theoretical study. In another study, the electronic properties of GaAs/AlGaAs asymmetric triangular double quantum well have been examined by Dahiya et al. [39]. Moreover, Zhao et al. [40] have studied the linear and nonlinear optical absorption coefficients and third-harmonic generation for AlGaAs/GaAs single and double triangular QWs structures. In their paper, Zhang et al. [41] have used a numerical method to calculate the depolarisation effect in the intersubband transitions of GaAs/AlxGa1−xAs triangular quantum wires. While the optical absorption coefficients and refractive index changes of a quantum wire with triangle cross section have been examined by Khordad et al. [42], Khordad and Tafaroji [43] have studied the second- and third-harmonic generations in GaAs triangle quantum wires. In other theoretical studies, Bahramiyan and Khordad [44] analysed the electron–phonon interaction’s effect on the optical properties of triangular quantum wires and the intersubband optical absorption and the refractive index changes in a GaAs/AlGaAs quantum wire with equilateral triangle cross section under the laser field effects have been investigated by Barseghyan et al. [45]. Radu and Duque [46] have studied how the laser field affected the intersubband third-order nonlinear susceptibility in GaAs/AlxGa1-xAs quantum wires with equilateral triangle cross section. In their theoretical work, Kasapoglu et al. [47] investigated the donor impurity states in a GaAs QD which had an equilateral triangle shape. Martínez-Orozco et al. [48] have presented a study about the electron states and the related linear and nonlinear light absorptions and the changes in the index of refraction in vertically arranged coupled two-dimensional triangular QDs. Pavlovic and Peeters [49] have calculated the electronic structure of triangular and hexagonal MoS2 QDs by using the tight-binding approach.
Intrasubband-related linear and nonlinear optical absorption in single, double and triple QW: the compositions, temperature and QW’s number effects
Published in Philosophical Magazine, 2023
Redouane En-nadir, Haddou El-ghazi, Walid Belaid, Mohammed Tihtih, Hassan Abboudi, Ibrahim Maouhoubi, Anouar Jorio, Izeddine Zorkani
During the last decade, group III-N semiconductor alloys including InN, GaN and AlN and their ternary alloys InGaN and AlGaN have been widely studied. They are beneficial materials for optoelectronic engineering and energy harvesting due to their particular optical and electrical properties. Their wide and direct band gap covers almost the entire electromagnetic spectrum from infrared (IR) to ultra-violet (UV) passing through the visible light. These properties make them potential candidates for various applications in the optoelectronic market dominated by conventional semiconductors including silicon (Si) and gallium-arsenide (GaAs) and aluminium-gallium-arsenide (AlGaAs) (e.g. blue and green LEDs, laser diodes, photodetectors, solar cells, all types of switches, etc.) [1–5]. InGaN-based heterostructures are one of the few systems capable of providing band gaps ranging from 0.7 (InN) to 3.4 eV (GaN) [6,7]. The adjustment of the forbidden band could be achieved directly by modifying the In-content in the InGaN alloys. InGaN-based systems can cover almost the entire visible spectrum. Therefore, InGaN alloys could be a perfect candidate for optoelectronic devices that operate under harsh temperature, voltage and pressure conditions [8,9]. Due to a direct band gap, the absorption coefficient of InGaN alloys is very high and reaches 105 cm−1 for a photon energy of 0.5 eV above the absorption edge for all ranges of in-compositions [10]. One of the challenging lockouts of Group III-N materials, especially the InGaN alloy, is that it is difficult to grow a thick layer of this later on GaN due to the high mismatch rate between them. The thick matrix layer of GaN is usually developed to match different materials by dislocation, bending and annihilation. Although the lattice mismatch between GaN and InN is lower (only 10%) compared to InN/sapphire and GaN/sapphire, it is still sufficient to cause stresses at the InGaN/GaN [11]. However, there is a critical thickness for InGaN layers above which stresses are released by forming dislocations. This critical thickness is much lower for InGaN grown on a GaN substrate and it is less than 5 nm for in-compositions greater than 20% [12]. Once the critical thickness is reached, thread dislocations form, damaging the performance of the device. One of the suggested ideas to avoid this problem is to grow thin layers of InGaN (InGaN-quantum wells) on GaN instead of a thick layer. This will certainly influence the performance of the device such as the optical absorption, which is the subject of this study. Quantum wells are a type of low-dimensional system (e.g. quantum dots and quantum wire wells) that allow us to confine carrier charges (electrons and holes) [13].