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

Abstract

We present results of transport measurements performed on AlGaN/GaN heterostructures grown on silicon substrates. Variable temperature Hall effect measurements revealed that the temperature dependence of the carrier density and mobility were characteristic of a two-dimensional electron gas (2DEG). Carrier densities greater than 1×1013 cm−2 and Hall mobilities in excess of 1500 cm2/V s 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. SdH measurements were repeated and again no oscillations were present following illumination. However, exposing the samples to radiation from an 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. SdH oscillations were observed in one AlGaN/GaN on silicon carbide sample following exposure to radiation from an UV LED.

AlGaN/GaN HEMT grown on large size silicon substrates by MOVPE capped with in-situ deposited Si3N4

“…Current dispersion is one of the most serious problems in AlGaN/GaN HEMT and has been observed by various groups [7][8][9] [10][11][12][13] and also in-situ deposited insulating, p-type, n-type or low temperature GaN cap layers [14][15][16]. Promising results have been reported so far but ex-situ depositions are always carried out on a surface which has been exposed to air, while GaN passivation layers may lead to lower 2DEG density (7-8 Â 10 12 cm À2 ) [14][15][16] and consequently higher sheet resistance (4400 O/&).…”

Reduction of buffer leakage current in AlGaN/GaN high-electron-mobility-transistor structure on Si substrate by reducing the dislocation density in AlN buffer layer

“…It is found that the leakage current is much improved as the dislocation density in thin AlN buffer layer decreases. It has been successfully obtained the leakage current less than 10 -4 A/cm 2 layer between Si substrate and GaN epitaxial layer.…”

A magnetotransport study of AlGaN/GaN heterostructures on silicon

“…This approach has led to the growth of crack-free GaN films with total epitaxial thicknesses exceeding 2 µm. 17,18 The AlGaN/GaN on Si heterostructure field-effect transistors have demonstrated performance comparable to devices grown on other substrates. 19,20 While extensive progress has been made, many fundamental properties of AlGaN/GaN heterostructures are still not well understood.…”