This paper establishes the design space of III-N hot electron transistors (HETs) for high current gain by designing and fabricating HETs with scaled base thickness. The device structure consists of GaN-based emitter, base and collector regions where emitter and collector barriers are implemented using AlN and InGaN layers, respectively, as polarization-dipoles. Electrons tunnel through the AlN layer to be injected into the base at a high energy where they travel in a quasi-ballistic manner before being collected. Current gain increases from 1 to 3.5 when base thickness is reduced from 7 to 4 nm. The extracted mean free path (λ mfp) is 5.8 nm at estimated injection energy of 1.5 eV.

Establishment of design space for high current gain in III-N hot electron transistors

In this letter, we provide guidelines for the design of the base stack of a GaN-base HET suitable for high-frequency operation, through full band cellular Monte Carlo device simulations. The experimental curves are matched by our model and the transmission coefficient through the base is confirmed to be 0.2. We found that upon moderate reduction of the base thickness and collector barrier height, the transmission coefficient reaches values well above 0.5, hence allowing current amplification. The cutoff frequency of the scaled devices is then calculated from the short circuit current gain and is found to be larger than 100 GHz. Moreover, the cutoff frequency is seen to increase roughly proportionally to the transmission coefficient. This result, and the calculation of the base capacitance, suggests that the cutoff frequency can be well described by the intrinsic delay time $C_{b}/$ gm.

The Role of the Base Stack on the AC Performance of GaN Hot Electron Transistor

A study of transport in a quantum hot electron transistor made of an InAs/AlSb heterostructure is reported. It exhibited that the quantum hot electron transistors with a thick emitter efficiently prevented the parasitic base currents compared with transistors with a thin emitter. The static characteristics of the fabricated devices demonstrated an enhancement of the current gain of 9 and a collector breakdown voltage of 1.5 V with thick-emitter designed transistors. In optimized devices, the current is dominated by fast resonant tunneling that is promising for their future development of as high frequency transistors.

https://hal.archives-ouvertes.fr/hal-03015743/document

Study of resonant transport in InAs-based quantum hot electron transistors

The fabrication process of a hot-electron unipolar transistor with vertical transport based on InAs material is reported. Devices with an emitter width of 0.3 μm are fabricated and characterized. This submicrometer geometry allowed suppressing parasitic resistances and achieving high-current densities required for high-frequency operation. For the first time, for a hot-electron transistor, RF performances were achieved at room temperature. Cutoff frequencies of ft = 75 GHz and fmax = 88 GHz were obtained on devices transferred on an insulating substrate.

H. van Nguyen

Papers

Submicrometer Process and RF Operation of InAs Quantum Hot-Electron Transistors