Metalorganic gas control system for gas source molecular beam epitaxy

We have developed a new method to precisely control the small mass flow of low vapor pressure gases without a carrier gas in gas source molecular beam epitaxy. Group III metalorganic gases (TEA1, TEIn, and TEGa) were controlled by measuring the pressure difference at the flow element and giving feedback to the control valve. The beam pressure of source gases monitored at the growth position in a molecular beam epitaxy growth chamber had good linearity with the pressure difference at both sides of the flow element. The beam pressure was controlled with a maximum deviation of 2% for over 1 h of operation. The response of the beam pressure to changes in flow rate was quick with neither overshoot nor undershoot. The beam pressure could be reduced to 1/5 of its initial value in less than 5 s and then restored in less than 3 s. The source gases could be switched on and off abruptly. The rise time to 90% of the saturated beam pressure was less than 1 s and fall time to 10% of the saturated beam pressure was betw...