Hall Effect Measurement System for Characterization of Doped Single Crystal Diamond
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Hall Effect Measurement System for Characterization of Doped Single Crystal Diamond Isil Berkun1, Shannon N. Demlow1, Nutthamon Suwanmonkha1, Timothy P. Hogan1 and Timothy A. Grotjohn1,2 1 Michigan State University Electrical and Computer Engineering, East Lansing, MI, U.S.A. 2 Fraunhofer USA Center for Coatings and Laser Applications, East Lansing, MI, U.S.A ABSTRACT A temperature dependent Hall Effect measurement system with software based data acquisition and control was built and tested. Transport measurements are shown for boron-doped single crystal diamond (SCD) films deposited in a microwave plasma-assisted chemical vapor deposition (MPCVD) reactor. The influence of Ohmic contacts and temperature control accuracy are studied. For a temperature range of 300K-700K IV curves, Hall mobilities and carrier concentrations are presented. INTRODUCTION Diamond is a very promising material for high power, high temperature, high frequency electronic, as well as biotechnology applications. An important capability in the development of electronic grade boron doped diamond is the reliable determination of critical parameters such as the temperature dependent carrier concentration, mobility, and conductivity of the deposited diamond. High temperature Hall effect measurements help to better understand the samples and provide feedback on the fabrication processes. In this work, a high temperature Hall effect system was designed such that carrier concentrations and mobilities could be measured, as well as influences such as temperature stability and non-Ohmic contacts on the resulting measured values. EXPERIMENT A commercially available cryostat was modified by adding a custom designed sample stage consisting of an aluminum nitride plate on a heated copper stage. The system operates from room temperature to 700K and the samples are held under vacuum. Electrical connection to the sample is made using 25µm gold wires connected to metal contacts on the sample that were deposited using physical vapor deposition (PVD). Both van der Pauw and Hall bar geometries can be accommodated in this system. Samples of GaAs and boron doped diamond were measured in the system. In addition to reporting the measured properties of these samples, the open access design of the Hall effect measurement system was utilized to investigate the influence of temperature stability, and the influence of non-Ohmic contacts on the measured values. The boron doped diamond was deposited on 3.5 mm × 3.5 mm high pressure, high temperature (HPHT) substrates from Sumitomo Electric using a microwave plasma-assisted CVD reactor [1] as reported in previous investigations [2]. Samples are acid cleaned and hydrogen plasma etched prior to PVD deposition of gold near the four corners of the sample for van der Pauw measurements [3]. Samples are then oxygen plasma treated to remove surface conductivity effects.
Influence of temperature control: Temperature control was achieved by using the Ziegler Nichols method for determining the PID parameters [4]. For fixed temperatures
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