Silicon Substrate Removal of GaN DHFETs for Enhanced (<1100 V) Breakdown Voltage

In this letter, we present a novel approach to enhance the breakdown voltage
$(V_{\rm BD})$
for AlGaN/GaN/AlGaN double-heterostructure FETs (DHFETs), grown by metal–organic chemical vapor deposition on Si (111) substrates through a silicon-substrate-removal and a layer-transfer process. Before removing the Si substrate, both buffer isolation test structures and DHFET devices showed a saturation of
$V_{\rm BD}$
due to the electrical breakdown through the Si substrate. We observed a
$V_{\rm BD}$
saturation of 500 V for isolation gaps larger than 6
$\mu\hbox{m}$
. After Si removal, we measured a
$V_{\rm BD}$
enhancement of the AlGaN buffer to 1100 V for buffer isolation structures with an isolation gap of 12
$\mu\hbox{m}$
. The DHFET devices with a gate–drain
$(L_{\rm GD})$
distance of 15
$\mu\hbox{m}$
have a
$V_{\rm BD} > \hbox{1100}\ \hbox{V}$
compared with
$\sim$
300 V for devices with Si substrate. Moreover, from Hall measurements, we conclude that the substrate-removal and layer-transfer processes have no impact on the 2-D electron gas channel properties.