Ultrafast GaAs MOVPE growth for power electronics

Schottky diodes designed with negative breakdown voltages of up to 400 V are used in applications like power supplies, motor drives, battery charging and server/data centers. GaAs is an ideal choice for such devices. Due to its high electron mobilities, lower series resistance and thus lower power consumptions in the "on" state than using Si, GaN or SiC can be achieved. Also GaAs wafers are available up to 8” with extremely high quality and low etch pit densities. To achieve breakdown voltages above 200 V in GaAs, typically doping levels below 1*1015 cm-3 and thicknesses in the range of tens of micrometers are needed. In order to achieve minimum turnon losses, the thickness and doping has to be precisely controlled. For the epitaxy, the process time and group V precursor consumption due to typically high V/III ratios are the two largest cost factors. Recently, we have introduced MOVPE processes on a close coupled CRIUS showerhead reactor with growth rates up to 280 μm/h. Due to the extremely high growth rate, the loss of group-V material due to evaporation off the growth surface is minimized and even at V/III ratios below 15 a low C-background doping can be achieved. It is demonstrated that this low cost and ultrafast growth process is suitable for Schottky power diodes. 15 μm thick GaAs:Si Hall samples were grown at a growth rate of 100 μm/h. Controlled n-doping levels as low as 1.2*1014 cm-3 have been reached for a V/III ratio of 12. The room temperature mobilities were as high as 9*103 cm-3/Vs. Also, the electronic defect levels were analyzed by deep level transient spectroscopy. The EL2 (As anti-site) defect is found with a concentration 4.8*1014 cm-3. Nominally 20 μm and 30 μm thick layers were deposited on n-GaAs wafers for initial Schottky test diodes. The I-V curve in forward characteristics is characterized by an ideality factor of 1.2, a Schottky barrier height of 0.8 eV and a series resistance as low as 3.7 mΩcm2. Breakdown voltages above 370 V in reverse bias for doping levels of 2*1014 cm-3 were achieved proving the high potential of this approach.