Enhancement mode operation in AlInN/GaN (MIS)HEMTs on Si substrates using a fluorine implant

Abstract

We have demonstrated enhancement mode operation of AlInN/GaN (MIS)HEMTs on Si substrates using the fluorine plasma implant technique. The plasma RF power and treatment time was optimized to prevent the penetration of the fluorine into the channel region to maintain high channel conductivity and transconductance. An analysis of the threshold voltage was carried out which defined the requirement for the fluorine sheet concentration to exceed the charge at the dielectric/AlInN interface to achieve an increase in the positive threshold voltage after deposition of the dielectric. This illustrates the importance of control of both the plasma conditions and the interfacial charge for a reproducible threshold voltage. A positive threshold voltage of +3V was achieved with a maximum drain current of 367 mA/mm at a forward gate bias of 10V.

Nanoscale structural and chemical analysis of F-implanted enhancement-mode InAlN/GaN heterostructure field effect transistors

“…The chosen parameters are based on the previous study for obtaining an optimum positive threshold. 11 Finally, a Ni/Au (20/300 nm) gate metal layer was deposited prior to the fabrication of probe pad metals. The fabricated MISHFET had nominal dimensions of a 1.5 µm gate length, a 100 µm gate width, a 3.5 µm gate-source separation and a 10 µm gate-drain spacing.…”

“…These InAlN devices provide more freedom in barrier thickness design, since InAlN also has a larger spontaneous polarisation field. 11 This gives rise to a higher charge density in the 2DEG (two dimensional electron gas) and allows reduced barrier thickness which is advantageous for shorter gate length devices. This would also favour high speed operation and mitigate short-channel effects.…”

“…A number of approaches have been developed to obtain E-mode operation: for instance, a p-type GaN layer deposited on top of the AlGaN barrier under the gate 16,17 ; a recessed gate in which the barrier is thinned under the gate to deplete the 2DEG [18][19][20] ; and an implanted gate where atoms with large electronegativity, such as fluorine (F), are incorporated into the barrier, again to deplete the 2DEG. [11][12][13]15,[21][22][23][24][25] Each technique has its own associated advantages and drawbacks. In the recessed-gate thinning approach, the barrier depletes the 2DEG under the gate and thus shifts the threshold voltage in the positive direction, but at the same time it also reduces the mobility of carriers under the gate, resulting in a low drain current.…”

“…In the recessed-gate thinning approach, the barrier depletes the 2DEG under the gate and thus shifts the threshold voltage in the positive direction, but at the same time it also reduces the mobility of carriers under the gate, resulting in a low drain current. 11,16 The Fimplantation approach has been increasingly employed in the fabrication of E-mode devices since it was first reported for AlGaN-based HEMTs by Cai et al 24 4 -based plasma treatment, where a larger etching rate was found at a higher RF power (150 W). 22 Despite its wide applications as a critical technique in fabricating Emode devices, there is a lack of nanoscale understanding of material and device structures following the Ftreatment process, although such analysis could provide information to drive improvements in the device fabrication process and the optimization of device performance.…”

Normally-off p-GaN gate InAlN/GaN HEMTs grown on silicon substrates

“…Similarly, using fluorine treatment, gate recess, and ultrathin (e.g. 2 nm) InAlN barrier layers InAlN/GaN enhancement mode HEMTs have been realized [14][15][16] .…”