AlGaN/AlN-GaN-SL HEMTs with Multiple 2DEG Channels

We report on a multichannel approach for AlGaN/GaN high-electron-mobility transistors (HEMTs) to increase the carrier mobility in the low and high sheet carrier concentration regimes. Between the AlGaN barrier and GaN buffer, alternating thin layers of AlN and GaN were inserted to create multiple two-dimensional electron gas (2DEG) channels. All samples were grown by metalorganic vapor-phase epitaxy (MOVPE) on sapphire substrates and compared with conventional single-channel HEMT with the same sheet carrier concentration. For low total 2DEG carrier concentrations (<8 × 1012 cm−2), the mobility for the multichannel HEMT was enhanced due to a reduction of ionized impurity and dislocation scattering, which originates from a backbarrier effect of the underlying AlN layers. In the high total carrier concentration regime (>8 × 1012 cm−2), a mobility improvement is attributed to distribution of the sheet charge into multiple 2DEG channels. This has been found to reduce the carrier concentration per individual channel, which leads to larger distance between 2DEG and heterointerfaces and therefore less impact of interface roughness and alloy scattering. With increasing number of channels, phonon scattering is also reduced due to lowering of the three-dimensional (3D) electron density, which results from the added volume of the multiple 2DEGs. With this approach, the HEMT mobility was increased from 1620 cm2 V−1 s−1 to 1960 cm2 V−1 s−1 for a triple-channel device at sheet carrier concentration of 7.5 × 1012 cm−2.