Effect of Fixed Charges at Interface Between InP and Bonding Layer on Heterogeneous Integration of InP HEMTs

DC performances of depletion-mode 100 nm In _0.53 Ga _0.47 As/InP high electron mobility transistor (HEMT) heterogeneously integrated to silicon substrate by SiO ₂ -SiO ₂ bonding were investigated by using numerical simulation. Effects of fixed charges at the InP/SiO ₂ interface, the SiO ₂ /SiO ₂ bonding interface, and the SiO ₂ /Si interface on HEMT are compared. Among these charges, dc characteristics of HEMT are most sensitive to fixed charges at the InP/SiO ₂ interface. With the density of negative fixed charges at the InP/SiO ₂ interface increasing from - 5×10 ¹⁰ to - 1×10 ¹² cm ^-2 , the energy band exhibits an upward bending and leads to a decrease of electron concentration in the channel. The threshold voltage shifts from -1.03 to -0.85 V and the output current exhibits a decrease of 96 mA/mm under the gate bias of 0 V; meanwhile, the breakdown voltage increases from 4.4 to 6.5 V under the gate bias of -1.6 V. A shift of C- V curves in pace with transfer characteristic curves further confirms that the two-dimensional electron gas (2DEG) channel of HEMT is indeed influenced by fixed charges at the InP/SiO ₂ interface. As a comparison, the other two charges exhibit a relatively weak influence, where the increase of charges at the SiO ₂ /SiO ₂ bonding interface results in a 36 mV shift of threshold voltage and 20 mA/mm decrease of output current, and the charges at the SiO ₂ /Si interface only cause 6 mV shift of threshold that can almost be ignored. We proposed an appropriate increase of InP layer thickness to mitigate the impact of fixed charges on the transfer and output characteristic of HEMTs.