Room-Temperature Ballistic Transport in III-Nitride Heterostructures

Abstract

Room-temperature (RT) ballistic transport of electrons is experimentally observed and theoretically investigated in III-Nitrides. This has been largely investigated at low temperatures in low band-gap III-V materials due to their high electron mobilities. However their application to RT ballistic devices is limited by the low optical phonon energies, close to KT at 300 K. In addition, the short electron mean-free-path at RT requires nanoscale devices for which surface effects are a limitation in these materials. We explore the unique properties of wide-band-gap III-Nitride semiconductors to demonstrate RT ballistic devices. A theoretical model is proposed to corroborate experimentally their optical phonon energy of 92 meV, which is ∼ 4x-larger than in other III-V semiconductors. This allows RT ballistic devices operating at larger voltages and currents. An additional model is described to determine experimentally a characteristic dimension for ballistic transport of 188 nm. Another remarkable property is their short carrier depletion at device sidewalls, down to 13 nm, which allows top-down nanofabrication of very narrow ballistic devices. These results open a wealth of new systems and basic transport studies possible at RT.Ballistic transport has attracted huge interest of the research community since electrons can propagate through the semiconductor without random scattering from lattice defects, impurities and phonons. This regime was referred to as electron optics[1] and occurs when electrons travel a distance shorter than their mean free path L m , defined as the average distance travelled between consecutive scatterers.Semiconductors presenting very high electron mobility have been used as means to investigate ballistic and other transport phenomena. Most of these studies were undertaken at low temperatures where L m can be quite large, on the order of a few microns [2]. Moreover, low temperature operation was required due to the very low optical phonon energies, close to KT at 300 K, of semiconductors such as Arsenides and Antimonides. In addition, the conductance is quantized at low temperatures, fundamentally similar to the quantized Hall effect [3], where only a small number of transverse quantum channels are occupied. These effects have been explored and demonstrated in a number of different devices based on quantum interference [4,5], quantized conductance in a point contact [6,7], electron focusing [8], negative bend resistance [9,10], quenched and negative Hall effects [11], and lateral hot ballistic electron [12].While these devices were demonstrated under low temperature, ballistic transport at RT would open a pathway for many practical applications [13][14][15][16], offering a new design space for high frequency devices with quicker switching responses and lower dissipation losses than conventional devices. At RT however, L m is largely reduced, below 100 nm in some III-V semiconductors. This requires much smaller device dimensions, where surface effects can be a limiting factor [17]. The large ...

Magneto-ballistic transport in GaN nanowires

“…1) and w eff is the effective width of the nanowires. 16 We observed a change in the transport behavior from ballistic for V wire ( V knee % E OP =q (region I) to diffusive for V wire ) V knee (region III), with a transition region for V wire % V knee characterized by a strong non-linear behavior (region II). Such a clear signature of the electron interaction with optical phonons at E OP =q (which is also confirmed by the saturation of J) along with the amplitude of the negative bend resistance offers a tool to intrinsically investigate transport and scattering mechanisms in semiconductors and heterostructures.…”

“…Electrons moving diffusively between leads 2 and 1 generate a V 34 with the same sign of V 21 , since the device behaves like a voltage divider, while electrons moving ballistically are injected to the opposite lead without any scattering, thus generating V 34 with the opposite sign with respect to V 21 . 16 At 0 T and 4.2 K (Fig. 1), the signature of the ballistic transport was observed from the opposite sign of V 34 with respect to V wire around zero bias (region I), with a pronounced negative slope corresponding to a negative bend resistance R b ¼ V 34 =Jw eff , where J is the current density (shown in Fig.…”

“…15 The large optical phonon energy (E OP ) combined with the high electron mobility observed in wide band-gap GaN semiconductors allow the investigation of ballistic transport at larger voltages and temperatures than in other semiconductors. In this work, the ballistic filtering property of nanoscale crosses demonstrated on AlGaN/GaN heterostructures 16 was used to investigate the effect of a strong perpendicular magnetic field on the straight scattering-less trajectories of ballistic electrons, motivated by the strong analogy of ballistic transport in semiconductors and electrons moving in vacuum tubes 17 whose trajectory can be easily deflected by electromagnetic lens. Under large bias conditions (V bias ) E f =q, where E f is the Fermi energy), the presence of a perpendicular magnetic field caused electrons to move ballistically in cyclotron orbits, whose radius could be modified by sweeping either the applied bias or the magnetic field.…”

In-Plane-Gate GaN Transistors for High-Power RF Applications

“…Figure 3a shows the output characteristics of the 50 nmlong 85 nm-wide shallow IPGFET. A large current density (I ds /w) of 1.4 A/mm was observed, which is over 9x-larger than the best IPGFET [9] based on an InGaAs quantum well, due to the much larger carrier density and very small sidewall depletion in III-Nitrides [16,17]. Figure 3b shows the transconductance of the 50 nm-long IPGFETs, revealing larger and broader g m for wider nanowires.…”

Multi-channel tri-gate normally-on/off AlGaN/GaN MOSHEMTs on Si substrate with high breakdown voltage and low ON-resistance

“…5(c)], which agrees well with other reports in the literature. 32 The larger w dep for l of 1.5 lm is likely due to the greater strain relaxation within longer fins.…”