Magnetoresistance of n-GaAs at filamentary current flow

A large number of sharp structures are observed in the 4.2 K magnetoresistance of n-GaAs biased above impurity breakdown in a regime where current flow is filamentary. Most of the structures cannot be attributed to spectral properties of the semiconductor such as impact excitation of shallow donors or the magnetoimpurity effect. Experimental results give evidence that these structures are caused by a redistribution of the filamentary current flow when one filament border is swept across an imperfection in the material

Accelerating Neutron Tomography experiments through Artificial Neural Network based reconstruction

Neutron Tomography (NT) is a non-destructive technique to investigate the inner structure of a wide range of objects and, in some cases, provides valuable results in comparison to the more common X-ray imaging techniques. However, NT is time consuming and scanning a set of similar objects during a beamtime leads to data redundancy and long acquisition times. Nowadays NT is unfeasible for quality checking study of large quantities of similar objects. One way to decrease the total scan time is to reduce the number of projections. Analytical reconstruction methods are very fast but under this condition generate streaking artifacts in the reconstructed images. Iterative algorithms generally provide better reconstruction for limited data problems, but at the expense of longer reconstruction time. In this study, we propose the recently introduced Neural Network Filtered Back-Projection (NN-FBP) method to optimize the time usage in NT experiments. Simulated and real neutron data were used to assess the performance of the NN-FBP method as a function of the number of projections. For the first time a machine learning based algorithm is applied and tested for NT image reconstruction problem. We demonstrate that the NN-FBP method can reliably reduce acquisition and reconstruction times and it outperforms conventional reconstruction methods used in NT, providing high image quality for limited datasets

Technology and thermal stability of ALGAN/GAN HFETs

New approaches towards high reliable thermal stable ohmic and Schottky contacts for GaN/AlGaN-HFETs have been developed and implemented in device structures. The contact technology has been systematically optimized towards i) good electrical properties, ii) superior contact morphology and contour definition and Hi) high reliability and thermal stability. HFETs employing source/drain contacts based on WSiN diffusion barriers sandwiched between an Ti/Al/Ti/Au internal layer system and an overlayer metal as well as WSiN/Au and Ir/Au gate contacts have demonstrated long term stability at 400°C, Even after temperature storage tests at 500°C no significant device degradation could be detected. Ir/Au Schottky gates have found to be stable at the rather high level of Schottky barrier height of about 1.1 eV resulting in dramatically reduced leakage currents as compared to standard Pt/Ti/Au gate contacts to GaN-HFETs

Microstructuring of ion-implanted GaAs for high temperature sensor applications

Results are presented using deep ion implantation to microstructure the GaAs for sensor applications at in­creased ambient temperatures. Three selective etch­ing methods were used to micromachine ion-implanted GaAs with different implantation parameters and sub­sequent treatments. The corresponding membranes and cantilevers are fabricated

Mechanism of Power Density Degradation due to Trapping Effects in AlGaN/GaN HEMTs

International audienc

Hochbitratige Schaltungen mit InP-HBTs : Schlussbericht

[no abstract available

GaN-HEMT VSWR Ruggedness and Amplifier Protection

This paper presents the initial results in a study aimed at exploring the use of GaN-devices in applications where they are at risk of being exposed to high output voltage-standing-wave-ratio (VSWR) conditions. A measurement method developed to identify the limits of such stress is described together with the first results from measurements of novel FBH GaN-HEMT technology. Furthermore a circuit design aimed at preventing excessive operation under high output VSWR conditions is presented. The first findings suggest that the investigated devices are very robust to VSWR stress and the suggested protection circuit with a power-down cycle in the 100 ns range is sufficient to ensure a long lifetime with little degradation of RF performance