Tunneling Hot Electron Transistors Research Articles

Current gain above 10 in sub-10 nm base III-Nitride tunneling hot electron transistors with GaN/AlN emitter

We report on a tunneling hot electron transistor amplifier with common-emitter current gain greater than 10 at a collector current density in excess of 40 kA/cm2. The use of a wide-bandgap GaN/AlN (111 nm/2.5 nm) emitter was found to greatly improve injection efficiency of the emitter and reduce cold electron leakage. With an ultra-thin (8 nm) base, 93% of the injected hot electrons were collected, enabling a common-emitter current gain up to 14.5. This work improves understanding of the quasi-ballistic hot electron transport and may impact the development of high speed devices based on unipolar hot electron transport.

Common Emitter Current and Voltage Gain in III-Nitride Tunneling Hot Electron Transistors

Common-emitter operation was demonstrated in an N-polar tunneling hot electron transistor. Under collector-emitter bias of 7 V, small signal current gain ~1.3, and voltage gain ~4 were simultaneously obtained for transistors with 27.5-nm base. This is the first report of a III-nitride hot electron transistor with small signal current gain and intrinsic voltage gain both greater than unity. The result shows such III-nitride vertical transistors are promising for the next generation of high-frequency amplifiers.

Current gain in sub-10 nm base GaN tunneling hot electron transistors with AlN emitter barrier

We report on Gallium Nitride-based tunneling hot electron transistor amplifier with common-emitter current gain greater than 1. Small signal current gain up to 5 and dc current gain of 1.3 were attained in common-emitter configuration with collector current density in excess of 50 kA/cm2. The use of a combination of 1 nm GaN/3 nm AlN layers as an emitter tunneling barrier was found to improve the energy collimation of the injected electrons. These results represent demonstration of unipolar vertical transistors in the III-nitride system that can potentially lead to higher frequency and power microwave devices.

Negative differential resistance in GaN tunneling hot electron transistors

Room temperature negative differential resistance is demonstrated in a unipolar GaN-based tunneling hot electron transistor. Such a device employs tunnel-injected electrons to vary the electron energy and change the fraction of reflected electrons, and shows repeatable negative differential resistance with a peak to valley current ratio of 7.2. The device was stable when biased in the negative resistance regime and tunable by changing collector bias. Good repeatability and double-sweep characteristics at room temperature show the potential of such device for high frequency oscillators based on quasi-ballistic transport.

Compact multiple-valued multiplexers using negative differential resistance devices

Quantum electronic devices with negative differential resistance (NDR) characteristics have been used to design compact multiplexers. These multiplexers may be used either as analog multiplexers where the signal on a single select line selects one out of four analog inputs, or as four-valued logic multiplexers where the select line and the input lines represent one of four quantized signal values and the output line corresponds to the selected input. Any four-valued logic function can be implemented using only four-valued multiplexers (also known as T-gates), and this T-gate uses just 13 devices (transistors) as compared to 44 devices in CMOS. The design of the T-gate was done using a combination of resonant tunneling diodes (RTD's) and heterojunction bipolar transistors (HBT's) with the folded I-V characteristic (NDR characteristic) of the RTD's providing the compact logic implementation and the HBT's providing the gain and isolation. The application of the same design principles to the design of T-gates using other NDR devices such as resonant tunneling hot electron transistors (RHET's) and resonant tunneling bipolar transistors (RTBT's) is also demonstrated.

Multiple Negative Differential Resistance due to Quantum Interference of Hot Electron Waves in Metal (CoSi 2)/Insulator (CaF 2) Heterostructures and Influence of Parasitic Circuit Elements

We report the observation of multiple negative differential resistance (NDR) in a metal (CoSi2)/insulator (CaF2) resonant tunneling hot electron transistor structure. Multiple NDR observed here can be attributed to the modulation of the transmission probability of hot electron waves due to quantum interference in the conduction band of the insulator (CaF2) collector barrier layer between two metal (CoSi2) layers. By reducing the influence of the Schottky diode at the CoSi2/Si interface, relatively clear and low-voltage NDR is observed. It is found, by a simulation including parasitic elements, that the collector resistance and leakage current greatly influence the current voltage characteristics.

The growth of resonant tunneling hot electron transistors using chemical beam epitaxy

A systematic growth study of InGaAs/AlAs/InGaAsP resonant tunneling hot electron transistors (RHETs) was performed using chemical beam epitaxy (CBE). The resonant tunneling hot electron transistors studied consist of a highly strained AlAs/In 0.75Ga 0.25As/AlAs double barrier structure and an undoped InP collector barrier with 1.1 and 1.2 μm InGaAsP graded layers. These quaternaries were lattice matched to InP within 2.6×10 −4 and showed an averaged full width at half-maximum (FWHM) of 6 meV from low temperature photoluminescence (PL) measurement. The effects of growth interrupt were studied using PL, X-ray diffraction and secondary ion mass spectrometry (SIMS) measurements. It was found that excessive growth interrupt induced high oxygen accumulation (8×10 18 cm −3) at the heterojunction and reduced the intensity of PL spectra. Moreover, for the growth of tunneling heterostructures, low substrate temperature, appropriate growth interrupts and use of hydride drying filters and high purity hydrides were helpful to improve device performance. The highest peak-to-valley current ratio (PVR) observed was 12.7, and maximum base transport ratio was 0.98 at 80 K. Furthermore, some digital functions such as flip-flop gate and exclusive NOR were demonstrated using a single RHET.

InGaAs/AlAs/InGaAsP resonant tunneling hot electron transistors grown by chemical beam epitaxy

InP-based resonant tunneling hot electron transistors (RHET's) were studied systematically using chemical beam epitaxy (CBE) for the first time. All the RHET's studied have a highly strained AlAs/In/sub 0.75/Ga/sub 0.25/As/AlAs resonant tunneling double barrier as a hot electron injector, and an InP collector barrier with or without InGaAsP graded layers. The highest transport ratio (/spl alpha/) observed is 0.98, and the highest peak-to-valley current ratios (PVR's) measured are 20 and 200 in the collector current and base current, respectively, at 80 K. A self-consistent simulation is used as a reference to optimize the hot electron injector and to explain the ballistic transport. An energy spectrometer technique was applied to the RHET's for resolving the hot electron energy distribution which showed a full width at half maximum (FWHM) of around 58 meV, indicating ballistic transport of electrons. Finally, room temperature transistor action was also observed with a /spl beta/ of 4 and a cutoff frequency of 31 GHz. >

Novel Electronics Enabled by Rare Earth Arsenides Buried in III-V Semiconductors

ABSTRACTHeterostructures consisting of III-V semiconductors and epitaxial layers of the rare earth monoarsenides can be grown by molecular beam epitaxy. By alloying ErAs with ScAs, lattice match can be achieved with (Al,Ga)As. Using magneto-transport measurements, we show that these layers are semi-metallic with equal electron and hole concentrations, 3.0 ×1020 cm−3. Shubnikov-de Haas oscillations are used to confirm the predicted Fermi surface geometry and measure the electron effective mass and the coupling to the 4f spin on the Er3+ ion. Remarkably, the material shows no transition from semimetal to semiconductor as the film thickness is reduced to three monolayers. Below three monolayers the films are not uniform and are believed to consist of islands three monolayers high.This system provides a unique opportunity to explore novel electronics based on controlled transport through semimetal/semiconductor heterostructures. Lateral transport through semimetal islands immersed in a δ-doped layer may provide a fast non-linear material for THz electronics. Vertical transport through thin epitaxial layers may enable resonant tunneling hot electron transistors with a semi-metal base. Preliminary experiments on transistor like test structures measure some transfer through a 10 monolayer thick semimetal base. They also identify overgrowth of the III-V semiconductor on the semimetal layer as the key materials issue.

Transient analysis of resonant tunneling hot electron transistor (RHET)

We made a transient analysis of an InGaAs/In(AlGa)As resonant tunneling hot electron transistor (RHET) using time-dependent ensemble Monte Carlo simulation. We simulated the transient characteristics of electron transport in the collector barrier region and the collector current of the RHET. We accounted for the hot electron current and displacement current. We found that the collector current delay is about half the transit time due to the displacement current.

Resonant tunneling hot-electron transistor with current gain of 5

By optimizing its structure, we have improved the current gain and collector-current peak-to-valley ratio of a resonant tunneling hot-electron transistor. The device has an asymmetric resonant tunneling barrier with an optimal well thickness to attain a higher peak-to-valley ratio for the collector current. Also, the device uses a graded collector barrier and decreased base thickness, exhibiting a common emitter current gain of 5.1 (at 77 K), the highest value ever reported for an AlGaAs/GaAs hot-electron transistor.