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Sheet Density (sheet + density)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Optimization of homoepitaxially grown AlGaN/GaN heterostructures

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2010
J. A. Grenko
Abstract We report on the growth of Al0.25Ga0.75N/GaN heterostructures on low dislocation density semi-insulating c -axis GaN substrates by metalorganic vapor phase epitaxy (MOVPE). A room temperature (RT) Hall mobility (µRT) up to 2065,cm2,V,1,s,1 at sheet density (ns) of 8.25,×,1012,cm,2 has been measured. This work compliments prior studies in which we observed a buffer-induced modulation of the RT two-dimensional electron gas (2DEG) ns and µRT by varying the GaN buffer layer thickness. Here, we focus on the optimization of the heterostructure 2DEG properties by elimination of silicon doping in the Al0.25Ga0.75N barrier and unintentional Al in the not-intentionally doped (n.i.d.) GaN buffer layer. The 15% improvement in µRT and ns relative to previous results is consistent with those predicted by Poisson solver calculations. Use of thick GaN buffers has minimized the theoretical mobility reduction based on intersubband scattering and has enabled us to determine the 2DEG sheet density associated with the polarization field () to be ,5,×,1012,cm,2. [source]

Inside Back Cover (Phys. Status Solidi A 5/2010)

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2010
J. H. Leach
The Feature Article by Morkoē and co-workers (pp. 1091,1100) centers around the not so intuitive phenomena in two types of GaN based devices, namely InGaN based LEDs and InAlN barrier GaN heterojunction FETs. In terms of the LEDs, the paper uncovers that the quantum efficiency degradation observed at high current injection levels is not necessarily of Auger recombination origin. Furthermore, nearly similar behavior of LEDs on c-plane and mplane suggests that the main driving force for the efficiency degradation is not polarization induced field either. The data along with their interpretation should set the stage for an accurate physics- based model to be developed. In terms of the FETs, the authors show that there is an optimum sheet density, which depends on drain bias or the electric field in the channel, at which the LO phonon lifetime is shortest, the velocity is highest, and the device degradation is least. The average optimum density is near 7 × 1012 cm,2 which challenges the proverbial notion that the higher the sheet density the better it is. Another outcome of this discussion is that heat dissipation takes the route of hot electrons giving off heat to LO phonons which in turn give it to LA phonons when they decay. Naturally, the shortest LO phonon lifetime is best for heat removal and thus the devices are more reliable in addition to electrons traversing at the highest velocity. [source]

Effect of non-abrupt doping profiles on the carrier sheet density in one-side modulation-doped GaAs/AlGaAs quantum wells

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2004
F. M. S. Lima
Abstract A theoretical study on the influence of non-abrupt doping profiles on the electronic subband structure in one-side modulation-doped GaAs/AlGaAs quantum wells with graded interfaces is presented. Emphasis is given on the dependence of the carriers sheet density on both the spacer thickness and the donors diffusion length. A proper discretization method for solving the coupled Schrödinger and Poisson equations self-consistently over a nonuniform grid is proposed. This furnishes numerically stable results for the electron sheet density even when non-abrupt doping and heterointerface profiles are included in the model calculation. The depletion approximation is surpassed and a significant increase in the electron sheet density is obtained when non-abrupt doping profiles are taken into account. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]