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The effect of defects and interfacial stress on InGaAs/GaAs heterojunction FET reliability
Published in G B Stringfellow, Gallium Arsenide and Related Compounds 1991, 2020
We have performed a two-dimensional PL imaging experiment in order to assess possible “phonon-wind” driven transport, and find no evidence for this type of transport (shell-shaped PL distributions). However, one possible mechanism for our power-dependent transport is similar to modulation-doping. Our low-power mobilities at each temperature are similar to classically obtained mobilities dominated by ionized-impurity scattering, and are very nearly identical in both samples. At higher laser powers the increase in mobility may result from both an increase in carrier density and the charge neutrality of excitons. Thus, for example, excitons are insensitive to Coulomb scattering, and may thus have large mobilities. Further, the photoexcitation of additional free carriers may overwhelm, or screen out, the residual impurities in the GaAs, thus yielding larger mobilities. These effects are similar to that observed in modulation-doped structures, whereby Coulomb scattering is significantly reduced. In electrical transport measurements, for every charge carrier there is a charged impurity. The advantage of modulation- doping is that this charged impurity is spatially removed from the charged carrier conduction channel. In our transport technique, photoexcitation may generate many times more carriers than there are residual impurities, thus simulating modulation doping, and allowing studies of absolute mobility limits.
Breakdown Voltage Improvement Techniques in AlGaN/GaN HEMTs
Published in D. Nirmal, J. Ajayan, Handbook for III-V High Electron Mobility Transistor Technologies, 2019
In high electron mobility transistors (HEMTs), which are also called modulation-doped field-effective transistor (MODFETs), the modulation doping is achieved by doping a wide band gap semiconductor layer grown adjacent to a narrow band gap semiconductor to form a junction between two materials with different band gaps as the channel instead of doped region. The two dissimilar compound semiconductor materials, which are grown one above the other, form a heterostructure, thus it is also called a heterostructure FETs. AlGaN/GaN high-electron-mobility transistors (HEMTs) have received much attention for their ability to operate at high-power levels [1]. They are very useful components for the development of base stations in the telecommunications networks and for civil, military and space radar applications. There are several economic and technological stakes, which require the development of suitable techniques for failure analysis on GaN-based HEMTs. The failure analysis techniques implemented for GaAs components are not directly transposable to the GaN components [2–6] because of the different band gaps of the two semiconductor materials.
Introduction to Computational Electronics
Published in Dragica Vasileska, Stephen M. Goodnick, Gerhard Klimeck, Computational Electronics, 2017
Dragica Vasileska, Stephen M. Goodnick, Gerhard Klimeck
The development of molecular beam epitaxy (MBE) [30] (see Figure 1.7) has been pushed by device technology to achieve structures with atomic layer dimensions and this has led to an entirely new area of condensed matter physics and the investigation of structures exhibiting strong quantum size effects. MBE has played a key role in the discovery of phenomena like two-dimensional electron and hole gases, quantum Hall effect [31], and new structures like quantum wires and quantum dots, etc. The continued miniaturization of solid-state devices is leading to the point where quantization-induced phenomena become more and more important. These phenomena have shown that the role of material purity, native defects, and interface quality are very critical to device performance. Modulation doping is employed to achieve adequate carrier densities in one region of the device that is physically separated from the source of the carriers, the ionized impurities.
Numerical Study of Two HEMTs, AlGaN and InGaN, by Sharing the Drain Area for Power Application
Published in IETE Journal of Research, 2023
Bechlaghem Fatima Zahra, Hamdoune Abedelkader
First, GaN can form type I heterojunction with ternary compounds like AlGaN and InGaN enabling the use of modulation doping techniques in HEMT devices. Second, the lattice mismatch between GaN and AlN can be exploited to modify the carrier concentration at their interface [5]. One of the most interesting properties of these devices is the formation of two-dimensional electron gas (2-DEG) with very high electron mobility at the hetero interface. AlGaAs/GaAs HEMTs are candidates for high speed and mm wave applications. InGaN-based HEMTs have attracted much attention for application in high-frequency and high-power devices due to the large bandgap, the high drift electron velocity, and the high breakdown electric field of III-N materials. Significant improvements in the fabrication and performance of HEMTs have stimulated a considerable interest in the modeling of such structures [6]. In this work, we demonstrate that it is possible to obtain excellent properties with minimal side effects in the technology and performance of two HEMTs AlGaN and InGaN on H4-SiC substrate by sharing the drain area through optimization of the device design.
Thermoelectric materials and applications for energy harvesting power generation
Published in Science and Technology of Advanced Materials, 2018
Ioannis Petsagkourakis, Klas Tybrandt, Xavier Crispin, Isao Ohkubo, Norifusa Satoh, Takao Mori
Recently, there have been notable studies on composite thermoelectric materials in general. Initially for some inorganic systems, enhancement of the power factors through mechanisms like energy filtering [102] or modulation doping [103] have been proposed. There has also been enhancement observed for highly conducting metallic networks doped into ceramic borides, for example [104]. To get a simple general picture of organic–inorganic hybrid TEs without including any such exotic effects, we first suppose a certain size of spherical inorganic TE particles mixed with organic materials (Figure 14). It can be assumed that we can obtain the generated TE power from the inorganic TE particles when the inorganic TE particles network for electric conduction. Herein, we can classify the volume ratio of inorganic TE particles into three regions: (1) non-networking region for the low volume ratio, (2) networking region for the middle volume ratio, and (3) reverse region for the high volume ratio. In the non-network region, it can be expected that the inorganic TE particles do not assist the TE performances. In contrast, as far as we assume spherical particles, the reverse region is not our interest because the inorganic TE materials do not obtain flexibility. Thus, the hybrid effect should be observed in the network-forming region. The maximum ratio for the network-forming region is around 74 % where the spherical particles give the closest packing fulfilled with the organic materials. In connection with the relation between the volume ratio and the packing style, the body-centered cubic packing, the primitive cubic packing, and the diamond cubic packing develop at the ratio of 68 %, 52 %, and 34 %, respectively. It suggests that the inorganic TE particles have the potential to output generated power in the wide volume ratio from 34 % to 74%. To optimize the TE performances, we need to choose the appropriate particle sizes to utilize the mean free paths of electron and phonon because the particle network for electric conduction can also conduct heat. In similar systems, such as electrically conductive adhesives; metal-resin composites, and thermal conductive sheets; filler-silicone composites, percolation theory explains electric and thermal conductions, where the interfacial resistances play the dominant role [105,106].