AlGaN/GaN HEMT grown on large size silicon substrates by MOVPE capped with in-situ deposited Si3N4
AlGaN/GaN high electron mobility transistors (HEMTs) have been grown on 4 and 6 in Si(1 1 1) substrates by metal organic vapor phase epitaxy (MOVPE). A record sheet resistance of 256 Ω/□ has been measured by contactless eddy current mapping on 4 in silicon substrates. The wafer also shows an excellent uniformity and the standard variation is 3.6 Ω/□ over the whole wafer. These values were confirmed by Hall–Van der Pauw measurements. In the 2DEG at the AlGaN/GaN interface, the electron mobility is in the range of 1500–1800 cm2/Vs and the electron density is between 1.3×1013 and 1.7×1013 cm−2. The key step in obtaining these results is an in-situ deposited Si3N4 passivation layer. This in-situ Si3N4, deposited directly after AlGaN top layer growth in the MOVPE reactor chamber, not only prevents the stress relaxation in AlGaN/GaN hetero-structures but also passivates the surface states of the AlGaN cap layer. HEMT transistors have been processed on the epitaxial structures and the maximum source–drain current density is 1.1 A/mm for a gate-source voltage of 2 V. The current collapse is minimized thanks to in-situ Si3N4. First results on AlGaN/GaN structures grown on 6 in Si(1 1 1) are also presented.