Scattering mechanisms limiting two-dimensional electron gas mobility in Al0.25Ga0.75N/GaN modulation-doped field-effect transistors

Abstract

In order to characterize the electron transport properties of the two-dimensional electron gas (2DEG) in AlGaN/GaN modulation-doped field-effect transistors, channel magnetoresistance has been measured in the magnetic field range of 0–12 T, the temperature range of 25–300 K, and gate bias range of +0.5 to −2.0 V. By assuming that the 2DEG provides the dominant contribution to the total conductivity, a one-carrier fitting procedure has been applied to extract the electron mobility and carrier sheet density at each particular value of temperature and gate bias. Consequently, the electron mobility versus 2DEG sheet density has been obtained for each measurement temperature. Theoretical analysis of these results suggests that for 2DEG densities below 7×1012 cm−2, the electron mobility in these devices is limited by interface charge, whereas for densities above this level, electron mobility is dominated by scattering associated with the AlGaN/GaN interface roughness.

Ohmic Contact-Free Mobility Measurement in Ultra-Wide Bandgap AlGaN/AlGaN Devices

“…Increasing n 2DEG also moves the charge distribution closer to the interface, increasing its limiting effect on mobility [13], suggesting an increasing importance of alloy scattering and interface roughness scattering with increasing 2DEG density, consistent with our data. Summing ionised defect scattering, alloy scattering, and interface roughness via Matthiessen's rule produced an excellent phenomenological fit to the data, as shown in Figure 3.…”

The persistent photoconductivity effect in AlGaN/GaN heterostructures grown on sapphire and SiC substrates

“…[7][8][9]29,35,36 The increments in mobility due to photoexcitation at a fixed temperature can be attributed to the increased electron mean energy with an increasing carrier density in the 2DEG channel, which leads to an improved screening and thereby reduced scattering between the 2DEG electrons with the ionized donor impurities. 24,29 The 9 These results show that there are considerable compressive strains that exist in our GaN layers due to the mismatch between the epilayers.…”

“…35,36 After the deposition of these layers, a 20 nm thick undoped Al 0.20 Ga 0.80 N layer was grown on an AlN barrier layer at 1050°C and, finally, a 3 nm GaN cap layer was grown at the same temperature. At the beginning of the growth, the substrate was baked in H 2 ambient conditions at 1100°C for 5 min in order to remove the native oxide.…”

Subthreshold Mobility in AlGaN/GaN HEMTs

“…The differences in these contributions stems from a dimensionality difference in the scattering from a charged point or from a line of charge. The total mobility is the combination of all the different independent mobility limiting mechanisms, which can be approximated using Matthiessen's rule [16]. If one scattering mechanism dominates we can ignore other contributions.…”