High‐frequency InAlN/GaN HFET with f _max over 400 GHz

Abstract

Ultra-thin InAlN/GaN heterostructure field-effect transistors (HFETs) having high maximum oscillation frequency (f max) are fabricated by scaling lateral dimensions. A 3 nm GaN cap layer is adopted to reduce the electron density and suppress the short-channel effects. Non-alloyed regrown n +-GaN ohmic contacts with total ohmic resistance (R tot) of 0.13 Ω.mm is also introduced into the device, in which the virtual source-to-drain distance is 600 nm. T-shaped gate with 40 nm length is formed in the centre of the source-to-drain region by self-aligned e-beam lithography. The peak extrinsic transconductance (g m) reaches 956 mS/mm. Most of all, a high f max of 405 GHz is obtained, which is the highest value among the reported InAlN/GaN HFETs. These obtained results mean that the InAlN/GaN HFETs having reliability should be still suitable for G-band (140-220 GHz) power-amplifier application with further optimisation.

Origin(s) of Anomalous Substrate Conduction in MOVPE-Grown GaN HEMTs on Highly Resistive Silicon

“…Crucially, apart from thermal conductivity, the power loss due to this channel has been alleged to be the remaining bottleneck 18,19 for the high-frequency performance (i.e., maximum power gain frequency and power output) of record-breaking GaN-on-Si HEMTs 20,21 still lagging behind the devices grown on SiC. 22,23 With several mutually exclusive theories being discussed in the scientific community, both the origin and the identity of this unintentional substrate conductivity in metal-organic vapor phase epitaxy (MOVPE)-grown heterostructures have always been controversial. For instance, an inversion layer of electrons 24,25 arising from an abrupt AlN/Si interface and oxynitride acceptor traps 26 due to a nonideal AlN/Si interface have both been independently proposed to explain the presence of mobile carriers.…”

“…In this context, though the ill-effects of the AlGaN buffers in the form of leakage , and trapping , are now relatively well understood and controlled, the suspected association of the AlN nucleation layer with the formation of a conductive channel at the AlN/Si interface is still under debate. Crucially, apart from thermal conductivity, the power loss due to this channel has been alleged to be the remaining bottleneck , for the high-frequency performance (i.e., maximum power gain frequency and power output) of record-breaking GaN-on-Si HEMTs , still lagging behind the devices grown on SiC. , …”

High‐voltage AlInN/GaN superjunction fin‐gate high electron mobility transistor for power‐switching application

“…The AlInN/GaN heterostructure can be strain free and address better reliability than the conventional AlGaN/GaN devices [4]. Additionally, due to the strong polarization in the AlInN layer, the AlInN/GaN HEMT always has higher 2DEG density and thinner barrier, leading to higher output power, transconductance and cut-off frequency [5][6][7][8][9][10][11][12]. However, the conventional planar HEMTs suffer from the intrinsically depletion-mode operation and buffer leakage current.…”

Pulsed sputtering selective epitaxial formation of highly degenerate n-type GaN ohmic contacts for GaN HEMT applications

“…14,15) In MOCVD processes, surface diffusion of precursors from mask regions compromises the uniformity of the regrown GaN. 16,17) Furthermore, MOCVD growth of highly Si-doped GaN often proceeds in the Stranski-Krastanov mode due to the antisurfactant effect of Si dopant, adversely degrading the structural and electrical properties of the material. 18,19) The MBE technique has yielded impressive results in the regrowth of highly n-type doped ohmic contacts for GaN HEMT applications.…”