Papers by Author: Anna Piotrowska

Abstract: In this work the electrical properties of Ni and Ni₂Si contacts on n-type 4H-SiC were correlated to the strong structural changes at the contact/SiC interface upon annealing. We can conclude that only δ-Ni₂Si grains play a main role in determining electrical transport properties of the Ni-based ohmic contacts to n-SiC. It is presumed that a recrystallization and texturization of δ-Ni₂Si phase on (0001)SiC-surface during high temperature annealing (> 900°C) contributes to the change of barrier heights, as well as specific contact resistance of contacts.

Abstract: The stability of Au wire connections to n-SiC/Ti ohmic contacts and to n-SiC/Ni ohmic contacts with top Au or Pt layers has been investigated. Long-term tests of the connections are performed in air at 400oC. Evaluation of electrical parameters, morphology and structure of the metallization as well as the strength of Au joint show stable Au wire bonds to the metallization with Ti-ohmic contacts.

Abstract: The reliability of Ni2Si/n-SiC ohmic contacts with Au overlayer either without or with Ta-Si-N diffusion barrier was investigated after long-time aging in air at 400oC and rapid thermal annealing in Ar up to 800oC. It is shown that aging of the Au/Ni2Si/n-SiC contacts in air at 400oC resulted in complete degradation due to both oxygen penetration and interdiffusion/reaction processes. In contrast, only a small change in properties was detected on the contacts annealed in Ar at 800°C. The stability of both electrical and structural properties of Au/TaSiN/Ni2Si/n-SiC thermally stressed contacts at different conditions points out their superior thermal stability.

Abstract: Presented are the results of studies on Ti-Al-N MAX phase formation in thin film multilayers of Ti, Al and TiN deposited on n-type GaN by magnetron sputtering. Two approaches to phase formation are shown, annealing Ti-Al-TiN multilayers at 600oC in argon and annealing Ti/Al multilayers at 600oC in nitrogen. Samples are characterized by means of High Resolution X-Ray Diffraction and Secondary Ion Mass Spectrometry profiling. As MAX phases are very stable at high temperatures the potential of their application as ohmic contacts to n-GaN devices is discussed.

Abstract: In this study, the formation of Ni, Ni-rich Ni2Si and Si-rich NiSi2 ohmic contacts to n-type 4H-SiC are investigated. The Ni/n-SiC ohmic contact with resistance rc ~ 4.2×10-4 Ω cm2 is formed after annealing at 1050oC. For Ni2Si/n-SiC, the contact resistances were rc ~ 4×10-4 Ωcm2 and rc ~ 3.5×10-4 Ωcm2 after annealing at 1000 and 1050oC, respectively. The non-ohmic I-V characteristics are observed for NiSi2/n-SiC contact even after annealing at 1050oC. The features of ohmic contact formation for Ni-based metallization to 4H n-SiC are discussed.

Abstract: The kinetics of 4H-SiC thermal oxidation by RTP technique and the properties of thin thermal oxide was reported. The thickness of the thermal oxide was determined by spectroscopic ellipsometry and confirmed by electrical measurements. The conductance method was applied to analyse the surface states parameters. The lifetime, density and cross-section of the surface traps were extracted for as-fabricated MOS capacitors and after thermal annealing processes.

Abstract: Fabrication of surface-relief microstructures in GaSb for application in mid-infrared optoelectronic devices is described. Photo- and e-beam lithography was used to define patterns on GaSb surfaces. Ar/O2 sputter etching and RIE in BCl3-based plasma were applied to transfer preshaped master into the GaSb substrate. Circular microlenses with an aspect ratio (height to diameter) 0.4/10 µm and circular gratings with 0.4 µm linewidth / 1 µm period and 1.7 µm depth have been demonstrated.