Threshold voltage scattering of GaAs MESFET's fabricated on LEC-grown semi-insulating substrates

Abstract

Threshold voltage standard deviation ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sigma V_{th}</tex> ) for MESFET's on a liquid encapsulated Czochralski (LEC) grown GaAs wafer was investigated, in connection with dislocation distribution. Threshold voltage (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</inf> ) scattering was found to be strongly correlated to the dislocation cell network structure in the substrate. This dislocation cell network is characteristic of the LEC-grown crystal. At large <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sigma V_{th}</tex> region, strongly networked dislocation cell structure was observed. In the area where dislocations distributed randomly without network structure, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sigma V_{th}</tex> was small in spite of high dislocation density. For FET's located in the dislocation-free region inside the network cell, low drain current I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds</inf> and high V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</inf> were recognized directly by a curve tracer. The experimental results regarding the dislocation network effect on V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</inf> scattering are discussed along with cathodoluminescence study results.