A compact electron beam evaporator for carbon doping in solid source molecular beam epitaxy

A new type of carbon source using the electron evaporator principle to generate a molecular beam is presented. The electrons are extracted from a hot tungsten filament which is biased negatively up to 1500 V versus the carbon target (ground potential), made from ultrapure pyrolytic graphite. The emission current at a fixed high voltage is controlled via a feedback loop and used to tune the carbon flux. In this way, a flux reproducibility of +/- 5% is achieved over a working period of 5 months. Flux rates up to 6.1 x 10(11) cm(-2) s(-1) at a source-sample distance of 250 mm have been achieved. The source design is very compact so it was possible to build it onto a flange with a inner diameter of 40 mm (CF40 flange) which saves mounting space. Using this source it was possible to prepare two dimensional hole gases with hole mobilities up to 160 000 cm(2) V-1 s(-1) at 1 K. No memory effect was observed. (C) 1999 American Institute of Physics. [S0034-6748(99)00808-4].