Ghulam Ishaq Khan Institute of Engineering Sciences and Technology

About: Ghulam Ishaq Khan Institute of Engineering Sciences and Technology is a education organization based out in Topi, Pakistan. It is known for research contribution in the topics: Thin film & Quantum efficiency. The organization has 618 authors who have published 940 publications receiving 10674 citations.

Polarization-dependent hole generation in 222 nm-band AlGaN-based Far-UVC LED: a way forward to the epi-growers of MBE and MOCVD

Abstract: Far-ultraviolet-C (Far-UVC) light-emitting-diodes (LEDs) offer a promising technology for the disinfection of surface, air, water, food and airborne disease transmission in occupied spaces, including COVID-19 (SARS-CoV-2) and other viral diseases, when it is meticulously designed, engineered, and applied. Research should continue on both the safety and efficacy of AlGaN-based Far-UVC LEDs, as well as the material choices and device designs to develop highly efficient solid-state UV germicidal irradiation (UVGI) at 222 nm emission to replace toxic low-pressure mercury lamps emitting at 253.7 nm. However, the key issue of hole concentration inside the multi-quantum-wells (MQWs) of AlGaN-based Far-UVC LEDs with high Al-contents is quite critical. Therefore, theoretical studies of AlGaN-based Far-UVC LEDs may suggest sufficient evidence for immediate consideration and implementation for the epitaxial growth of 222 nm-band Far-UVC LED technology during this world-wide health crisis. In this paper, the initial design of the Al-graded p-AlGaN hole source layer (HSL) on the performances of Far-UVC LED was compared with conventional bulk p-AlGaN HSL (non-graded)-based LED devices. For the evaluation of the device's performances, the energy band diagram, internal quantum efficiency (IQE), electrons and holes concentration, radiative recombination rate, and current density vs voltage characteristic were compared. It was found that LEDs at 222 nm emission without using the undoped (ud)-AlGaN final-quantum-barrier (FQB) and only keeping the Al-graded Mg-doped p-AlGaN HSL showed high carrier injection into the MQWs. The variation in the energy band diagram around the p-AlGaN electron-blocking layer (EBL)/p-AlGaN HSL region and p-AlGaN HSL/p-GaN contact-layer (CL) indicates that the introduction of the Al-graded p-AlGaN HSL, as well as the special choice of Al composition at the interfaces, are quite promising for the enhancement of hole injection toward MQWs. The simulation results suggest that the proposed structure of the Al-graded p-AlGaN HSL after omitting the ud-AlGaN FQB structure in the Far-UVC LED is quite useful for achieving high peak efficiency, as well as for suppressing the efficiency droop when compared to the conventional bulk Far-UVC LED. After introducing a new design of 40 nm-thick p-AlGaN HSL in the Far-UVC LED, the radiative recombination rate in the first two quantum-wells of MQWs has been improved up to ∼50%. The enhanced radiative recombination rate is attributed to the enhanced level of electron and hole concentrations by ∼26% and 53%, respectively, in the MQWs. Ultimately, after removing the ud-AlGaN FQB and using 40 nm-thick Al-graded (Al: 100% to 20%) p-AlGaN HSL, the efficiency droop has been remarkably reduced from ∼39% (Bulk-LED) to ∼19% in the new design of Far-UVC LED structure.

Proactive Uplink Interference Management for Nonuniform Heterogeneous Cellular Networks

Abstract: In homogeneous cellular networks, fractional power control (FPC) is employed to partially compensate the path-loss and, hence, improve uplink ( $U_{L} $ ) signal-to-interference ratio (SIR). However, this scheme is less effective in heterogeneous cellular networks (HetNets) because: (i) except the typical user, all other users with variable $U_{L} $ transmit power (UTP) act as interferers, (ii) FPC leads to high UTP by edge users and, hence, more interference, and (iii) small base stations (SBSs)’ densification further increases network interferences. Leveraging FPC in HetNets, we propose nonuniform SBS deployment ( $\text {NU-SBS}_{\mathcal {D}} $ ) to reduce interference and, thus, increase network performance. According to our $\text {NU-SBS}_{\mathcal {D}} $ model, SBS deployment ( $\text {SBS}_{\mathcal {D}} $ ) near macro base station (MBS) is avoided, whereas MBS coverage edge area is enriched with ultra-dense $\text {SBS}_{\mathcal {D}} $ . $\text {NU-SBS}_{\mathcal {D}} $ model leads to: (i) better SIR reception of MBS coverage edge users, (ii) fewer $\text {SBS}_{\mathcal {D}} $ requirement, and (iii) better SBS coverage in the MBS coverage edge area. Moreover, to make a model more proactive, we also consider reverse frequency allocation (RFA) to further abate both $U_{L} $ and downlink $(D_{L}) $ interferences. The coverage probability expressions are derived for both uniform SBS deployment ( $\text {U-SBS}_{\mathcal {D}} $ ) and $\text {NU-SBS}_{\mathcal {D}} $ while using RFA and FPC. Through simulation and numerical results, we characterize coverage probability for different values of SIR threshold, path loss compensation factor, SBS density, users density, and the distance between the typical user and the associated base station. The proposed $\text {NU-SBS}_{\mathcal {D}} $ model along with RFA leads to reduced network interference as compared with $\text {U-SBS}_{\mathcal {D}} $ and, thus, leverages FPC in HetNets.

Spectrum efficiency in CRNs using hybrid dynamic channel reservation and enhanced dynamic spectrum access

Abstract: Blocking of new arriving services and dropping of ongoing services are inherent problems in Cognitive Radio Networks (CRNs), which need to be addressed to enhance spectrum efficiency. In particular, Secondary Users (SUs) undergo service degradation in the face of Primary Users (PUs)’ arrivals. In this paper, we present a scheme called Efficient Spectrum Utilization (ESU) that reduces the dropping and blocking probabilities of existing and new services, respectively, to make efficient use of the available spectrum. The scheme divides the available spectrum into reserved and non-reserved bands. The reserved band is dynamically allocated a number of channels from the non-reserved band in order to accommodate those services which face interruptions while operating in the non-reserved band. The scheme renders dynamic access to the available spectrum and facilitates priority-based channel allocation and termination. SUs are divided into low and high priority levels depending on their Quality of Service (QoS) requirements. SUs with low priority level are granted direct access to both the bands to enhance channel utilization. SUs operating in the reserved band with high priority levels are granted uninterruptible status to ensure a certain level of service provisioning to SUs. The proposed ESU scheme is modeled using Continuous Time Markov Chain (CTMC) and mathematical expressions are derived for several QoS parameters. Performance of the proposed scheme is evaluated under various network conditions. Results demonstrate that ESU reasonably improves spectrum efficiency under channel failure in CRNs.

Pressure sensitive organic field effect transistor

Abstract: Thin films of organic semiconductor copper phthalocyanine (CuPc) and Al were deposited in sequence by vacuum evaporation on a glass substrate with Ag source and drain electrodes. The effect of pressure on the properties of the fabricated field effect transistor (FET) with metal (aluminum) – semiconductor (copper phthalocyanine) Schottky junction was investigated. It was observed that the drain–source resistance of this organic field effect transistor (OFET) decreased with pressure.