A compact and accurate analytical charge control model for finding gate capacitance of Al m Ga 1− m N/GaN MODFET is presented. This temperature dependent model incorporates the effect of strain relaxation, donor neutralization and free carrier generation in the Al m Ga 1− m N layer. Non-linear Fermi potential ( E F )-variation with the sheet carrier concentration ( n s ), and the charge induced in the two-dimensional electron gas (2-DEG) due to highly dominant effects of spontaneous and piezoelectric polarization at the heterojunction of MODFET are also considered. The model is based on closed form expression and does not involve any fitting parameter or elaborate computation. Agreement of calculated data with published simulated/experimental data proves the validity and applicability of the model.

Temperature and polarization dependent polynomial based non-linear analytical model for gate capacitance of AlmGa1−mN/GaN MODFET

We fabricated a multi-mesa-channel (MMC) structure by forming a periodic trench just under a gate electrode to improve the uniformity of effective electric field in the channel in an AlGaN/GaN high electron mobility transistor (HEMT). A unique performance, i.e., a nearly temperature-independent saturation drain current, was observed in the MMC device in a wide temperature range. A two-dimensional (2D) potential calculation indicates that the mesa-side gate effectively modulates the potential, resulting in a field surrounding 2D electron gas. Such a surrounding-field effect and a relatively lower source access resistance may be related to a unique current behavior in the MMC HEMT.

/pdf/nearly-temperature-independent-saturation-drain-current-in-a-2z8t5xp9kj.pdf

Nearly Temperature-Independent Saturation Drain Current in a Multi-Mesa-Channel AlGaN/GaN High Electron Mobility Transistor

densities greater than 1 x 10 13 cm -2 and Hall mobilities in excess of 1500 cm 2 /Vs were measured at room temperature. Variable field Hall measurements at low temperatures, and in magnetic fields up to 6 T, indicated that conduction is dominated by a single carrier type in these samples. Shubnikov de-Haas (SdH) measurements were also performed, but no oscillations were observed in fields up to 8 T and at temperatures as low as 1.2 K. Illuminating some of the samples with a blue (λ = 470 nm) light emitting diode (LED) induced a persistent increase in the carrier density. Shubnikov de-Haas measurements were repeated and again no oscillations were present following illumination. However, exposing the samples to radiation from an ultraviolet (UV) (λ = 395 nm) LED induced well defined SdH oscillations in fields as low as 4 T. The observation of SdH oscillations confirmed the presence of a 2DEG in these structures. It is hypothesized that small angle scattering suppressed the oscillations before exposure to UV light. This conclusion is supported by the observed increase in the quantum scattering time, τq, with the carrier density and the calculated quantum to transport scattering times ratio, τq/τc. For instance, in one of the samples the τq increased by 32% while the τc changed by only 3% as the carrier density increased; an indication of an increase in the screening of small angle scattering. The absence of SdH oscillations in fields up to 8 T and at temperatures as low as 1.2 K is not unique to AlGaN/GaN on silicon. This behavior was observed in AlGaN/GaN on sapphire and on silicon carbide. Shubnikov-de Haas oscillations were observed in one AlGaN/GaN on silicon carbide sample following exposure to radiation from a UV LED.

An electrical characterization of a two dimensional electron gas in GaN/AlGaN on silicon substrates

An analytical two-dimensional model for AlGaN/GaN HEMT with polarization effects for high power applications

Carrier transport in a set of AlGaN/GaN heterostructures from different sources with a range of carrier densities and mobilities has been investigated at low temperature and high magnetic fields. The Shubnikov-de Haas oscillations have been analysed to extract the quantum scattering lifetime, τq, and this is compared with the classical transport lifetime, τt, derived from the low-field mobility. The relationship between these parameters has been observed to depend systematically on the low-field mobility of the samples studied, and indicates that higher-mobility samples suffer less scattering from centres close to the two-dimensional conducting channel.

https://iopscience.iop.org/article/10.1088/0268-1242/16/5/321/pdf

Relationship between classical and quantum lifetimes in AlGaN/GaN heterostructures

Shubnikov-de Haas (SdH) oscillation and Hall measurement results were compared with HEMT DC and RF characteristics for two different MOCVD grown AlGaN-GaN HEMT structures on semiinsulating 4H-SiC substrates. A HEMT with a 40-nm, highly doped AlGaN cap layer exhibited an electron mobility of 1500 cm/sup 2//V/s and a sheet concentration of 9/spl times/10/sup 12/ cm at 300 K (7900 cm/sup 2//V/s and 8/spl times/10/sup 12/ cm/sup -2/ at 80 K), but showed a high threshold voltage and high DC output conductance. A 27-nm AlGaN cap with a thinner, lightly doped donor layer yielded similar Hall values, but lower threshold voltage and output conductance and demonstrated a high CW power density of 6.9 W/mm at 10 GHz. The 2DEG of this improved structure had a sheet concentration of n/sub SdH/=7.8/spl times/10/sup 12/ cm/sup -2/ and a high quantum scattering lifetime of /spl tau//sub q/=1.5/spl times/10/sup -13/ s at 4.2 K compared to n/sub SdH/=8.24/spl times/10/sup 12/ cm/sup -2/ and /spl tau//sub q/=1.72/spl times/10/sup -13/ s for the thick AlGaN cap layer structure, Despite the excellent characteristics of the films, the SdH oscillations still indicate a slight parallel conduction and a weak localization of electrons. These results indicate that good channel quality and high sheet carrier density are not the only HEMT attributes required for good transistor performance.

Carrier transport related analysis of high-power AlGaN/GaN HEMT structures

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Carrier transport related analysis of high-power AlGaN/GaN HEMT structures