Charge Density Based Small Signal Modeling for InSb/AlInSb Asymmetric Double Gate Silicon Substrate HEMT for High Frequency Applications

The Asymmetric Double Gate Silicon Substrate HEMT(ADG-Si-HEMT) is proposed in this article to analyse the carrier concentration and intrinsic small signal parameters for the heterostructure of the InSb/AlInSb silicon wafer DG-HEMT device. When the top and bottom gates are biased with different gate voltages, the HEMTs act as a three-port system and the device called Asymmetric Double Gate HEMT. The modulation of back-channel charge density due to the front gate voltage is analyzed with the position of quasi-Fermi energy levels(Ef). Also, the small signal model is obtained for various parameters like cut off frequency, gate to source capacitance and transconductance. The effects of the following parameters like delta doping, width of Silicon doping layer and various top and bottom gate voltages are analyzed to get enhanced device operation. The transconductance 2390 Sm/mm for Vfg=0.2V and cut off frequency around 197 GHz for Vbg=0.3 are obtained. All the analytical results are compared with Sentaurus 3-D TCAD simulation results. The asymmetric biasing technique offers various mixed application due to modulation in threshold voltage and modulating carrier density in dual channels.

Enhanced P-Type GaN Conductivity by Mg Delta Doped AlGaN/GaN Superlattice Structure

A method of combining the AlGaN/GaN superlattices and Mg delta doping was proposed to achieve a high conductivity p-type GaN layer. The experimental results provided the evidence that the novel doping technique achieves superior p-conductivity. The Hall-effect measurement indicated that the hole concentration was increased by 2.06 times while the sheet resistivity was reduced by 48%. The fabricated green-yellow light-emitting diodes using the achieved high conductivity p-type GaN layer showed an 8- and 10-times enhancement of light output power and external quantum efficiency, respectively. The subsequent numerical calculation was conducted by using an Advanced Physical Model of Semiconductor Device to reveal the mechanism of enhanced device performance. This new doping technique offers an attractive solution to the p-type doping problems in wide-bandgap GaN or AlGaN materials.

Colour centre generation in diamond for quantum technologies

Effective methods to generate colour centres in diamond and other wide band-gap materials are essential to the realisation of solid state quantum technologies based on such systems. Such methods have been the subject of intensive research effort in recent years. In this review, we bring together the various techniques used in the generation and positioning of colour centres in diamond: ion implantation, delta-doping, electron irradiation, laser writing and thermal annealing. We assess the roles and merits of each of these techniques in the formation of colour centres for different quantum technologies and consider future combinations of the techniques to meet the requirements of the most demanding applications.