Muhammad Usman

Energy efficiency improvements through heterogeneous networks in diverse traffic distribution scenarios

Energy Efficiency in cellular mobile radio networks has recently gained great interest in the research community. Besides the positive effect on global climate change, lowering power consumption of mobile networks is beneficial in terms of decreasing the operational cost for network operators. In this regard, the development of more energy efficient hardware and software components aside, effect of different deployment strategies on energy efficiency are also studied in the literature. In this paper, we investigate the energy efficiency improvements through different heterogeneous networks for both uniform and non-uniform traffic distribution scenarios. It has been shown that, using small power low base stations at the cell border decreases the power consumption significantly for both traffic scenarios and the most energy efficient deployment strategy highly depends on the area throughput demand of the system.

Time-resolved luminescence studies of proton-implanted GaN

Time-resolved photoluminescence measurements performed on proton implanted and annealed GaN layers have shown that carrier lifetime can be tuned over two orders of magnitude and, at implantation dose of 1×1015u2002cm−2, decreases down to a few picoseconds. With annealing at temperatures between 250 and 750u2009°C, carrier lifetime, contrary to electrical characteristics, is only slightly restored, indicating that electrical compensation and carrier dynamics are governed by different defects. Ga vacancies, free and bound at threading dislocations, are suggested as the most probable defects, responsible for electrical compensation and carrier lifetime quenching.

Energy efficient high capacity HETNET by offloading high QoS users through femto

Bandwidth, network performance, QoS and network power consumption are important dilemmas of contemporary telecommunication networks. With ever increasing demand for data services, networks are destined to become denser and more power hungry, essentially increasing the capital and operational expenditure for operators around the world. One of the technological remedies to this situation is heterogeneous networks. In this work, we present a promising attribute of heterogeneous networks by offloading high QoS indoor users through femto. Additionally, we take traffic demand and sparse network deployment into consideration. The traffic demand is expressed in terms of area spectral efficiency and the power consumed in network nodes is expressed in terms of area power consumption [1]. The results suggest that with an increase in femto density the area spectral efficiency of the considered LTE network increases and decreases monotonously for sparse networks. From an operators point of view, 100% offloading of premium users through femto is energy efficient at all area spectral efficiency targets. From an environmental perspective, 100% offloading of premium users is beneficial at low area spectral efficiency targets, while at high area spectral efficiency targets 40% offloading is energy efficient.

Stoichiometry of the ALD-Al2O3/4H-SiC interface by synchrotron-based XPS

The interface of Al2O3 with 4H-SiC is investigated with synchrotron-based high-resolution x-ray photoelectron spectroscopy to clarify the effect of post-dielectric deposition annealing processes (r ...

Interface analysis of p-type 4H-SiC/Al2O3 using synchrotron-based XPS

In this paper, the interface between Al2O3 and p-type 4H-SiC is evaluated using x-ray photoelectron spectroscopy (XPS) measurements. These studies are made on dielectric-semiconductor test structures with Al2O3 as dielectric with different pre-and post-deposition treatments. XPS measurements on the as-deposited samples with two different pre-surface cleaning have shown no formation of a SiO2 interlayer. However, after the post deposition rapid thermal annealing (RTA) at 1100 °C in N2O for 60s, a SiO2 interlayer is formed. The surface band bending was determined from Si 2p core level peak shifts measured using XPS. These results suggest that Al2O3 deposited on the p-type 4H-SiC have a net positive oxide charge which is complementary to that of n-type 4H-SiC. From these shifts it was found that the as-deposited RCA cleaned sample had an oxide charge of 5.6×1013 q/cm-2, as compared to standard cleaned samples, having 4.6×1013 q/cm-2. A further reduction in oxide charge was observed after annealing at 1100 °C in N2O, down to a value of 4×1013 q/cm-2.

Characterization of Al-Based High-k Stacked Dielectric Layers Deposited on 4H-SiC by Atomic Layer Deposition

Aluminum-based high-k dielectric materials have been studied for their potential use as passivation for SiC devices. Metal-insulator-semiconductor structures were prepared and their dielectric properties were analyzed using capacitance-voltage and current-voltage measurements. Atomic layer deposition was used for the deposition of dielectric layers consisting of AlN with or without a buffer layer of SiO2, and also a stack of alternating AlN and Al2O3 layers. It has been observed that AlN has a polycrystalline structure which provides leakage paths for the current through the grain boundaries. However, adding alternate amorphous layers of Al2O3 prevent this leakage and give better overall dielectric properties. It is also concluded that the breakdown of the dielectric starts from the degradation of the thin interfacial SiO2 layer.

A green router with built-in renewable energy module: Design, implementation and evaluation

Contemporary telecommunication systems are rapidly growing. High transmission speed and power consumption in such networks are an increasing concern. Therefore, building blocks of such networks need improvements in different aspects of their characteristics. In this paper we present an Open Source low power router which supports renewable energy by using an ultracapacitor based energy compatibility module. The described router achieves a packet rate of 580 kpps and a maximum throughput of 2.8 Gbps, consuming approximately 25 Watts. The energy compatibility module consists of a scalable design with low maintenance requirements. Our measurements show that the mentioned energy module has an efficiency of above 90%.

Effect of 3.0 MeV helium implantation on electrical characteristics of 4H-SiC BJTs

Degradation of 4H-SiC power bipolar junction transistors (BJTs) under the influence of a high-energy helium ion beam was studied. Epitaxially grown npn BJTs were implanted with 3.0 MeV helium in th ...

A Comparison of Free Carrier Absorption and Capacitance Voltage Methods for Interface Trap Measurements

This paper aims to establish a new method to characterize the interface between 4H-SiC and passivating dielectric layers. The investigations are made on MOS test structures utilizing Al2O3 and SiO2 dielectrics on 4H-SiC. These devices are then exposed to various fluences of Ar+ implantation and then measured by the new method utilizing optical free carrier absorption (FCA) technique to assess the interface traps. A program has been developed using MATLAB to extract surface recombination velocity (SRV) at the oxide/epi-layer interface from the optical data. Capacitance-voltage (CV) is done to extract the density of interface traps (Dit) and a comparison was made. It is observed that SiO2 samples show a large rise of SRVs, from 0.5×104 cm/s for a reference sample to 8×104 cm/s for a fluence of 1×1012 cm-2, whereas Al2O3 samples show more stable SRV, changing from 3×104 cm/s for the un-irradiated reference sample to 6×104 cm/s for a fluence of 1×1012 cm-2. A very similar trend is observed for Dit values extracted from CV measurements and it can therefore be concluded that the FCA method is a suitable technique for the interface characterization.

Effect of Nuclear Scattering Damage at SiO2/SiC and Al2O3/SiC Interfaces – a Radiation Hardness Study of Dielectrics

The radiation hardness of Al2O3 as a dielectric for SiC surface passivation is studied and compared to SiO2 for potential application in radiation hard SiC devices. SiO2 is deposited on 4H-SiC by PECVD and post annealed in N2O, whereas Al2O3 is deposited by atomic layer deposition (ALD). The oxides are bombarded with Ar ions in an energy range to produce maximum damage near the oxide/SiC interface. Metal-insulator-semiconductor structures are prepared and their dielectric characteristics are analyzed using capacitance-voltage measurements. Additionally, the effect of the interface damage on surface recombination is studied using the optical free carrier absorption method for the same samples. The results indicate that the SiO2/SiC interface is significantly affected at 1×1011 cm-2 fluence of Ar ions, however, the dielectric properties of Al2O3/SiC interface remain unaffected even for ten times higher fluences. Similar observations are made for the surface recombination measurements.