Triangular Barrier Diode Research Articles

Bidirectional bistability in a GaAs/AlGaAs double heterojunction triangular barrier switch (DHTBS)

A novel GaAs n +- n-δ( p +)- n- p +- n-δ( p +)- n- n + double heterojunction triangular barrier structure with two Al 0.3G 0.7As-doped barrier layers, exhibiting symmetrically bidirectional S-shaped negative differential resistance, has been successfully developed by molecular beam epitaxy. The occurrence of the bidirectional bistability switching behavior is caused by the potential redistribution due to the avalanche multiplication process within the reversely biased base-collector region. The possible mechanisms responsible for carrier transport are analyzed by an equivalent circuit including two triangular barrier diodes and an npn transistor. From experimental results, it is known that the environmental temperature plays an important role on the device performance. The influence of temperature on the switching parameters from 300 K to 150 K is also discussed.

Silicon Molecular Beam Epitaxy on Hydrogen-Plasma-Cleaned Substrates

A process sequence for low-temperature in situ processing of silicon in an ultra-high vacuum (UHV) multichamber system is presented. For substrate cleaning, a hydrogen/argon discharge plasma was produced with an UHV-compatible plasma source. This low-energy plasma was used to remove, in a single step, native oxide and organic contaminations from the wafer surface at low substrate temperatures (\\lesssim400° C). During the cleaning process the excitation energy of the gas atoms was determined by optical methods. The cleaning process was applied to patterned silicon substrates with micro-shadow masks. Local epitaxial growth by molecular beam epitaxy (MBE) on these substrates was used to fabricate triangular barrier diodes (TBD) to demonstrate the device quality for this cleaning procedure. The crystal quality of the grown layers and the interface was investigated by transmission electron microscopy (TEM). The electrical results for these diodes are in agreement with the grown layer sequence and the chosen dopings.

Vertical Si-Metal-Oxide-Semiconductor Field Effect Transistors with Channel Lengths of 50 nm by Molecular Beam Epitaxy

The growth conditions in molecular beam epitaxy (MBE) were studied for the fabrication of vertical Si-metal-oxide-semiconductor field effect transistors (MOSFET) with channel lengths down to 50 nm. The short channel length imposes severe constraints on the doping profile. MBE growth provided a steepness of 10 nm/dec for boron and 2 nm/dec for antimony. The sharpness of the doping profile was sustained throughout the process by keeping all process temperatures below 700° C. The high crystal quality and the well-defined doping profile was verified by the good performance of a triangular barrier diode. A vertical n-MOSFET with an estimated channel length of 50 nm was grown. The drain and gate characteristics were discussed for a source drain voltage regime from U sd=0 V to 1 V.

Energy oscillations in electron transport across a triangular barrier

Carrier transport across the semiconductor space-charge region of a silicon triangular barrier diode was investigated by a Monte Carlo simulation. Oscillations of the electron mean kinetic energy are observed as a function of position along the uphill slope of the barrier under bias. At a given point on the uphill slope, the energy distribution function shows an oscillatory behavior, with a periodicity corresponding to the optical phonon energy. These oscillations are shown to be due to the nonequilibrium dynamics of the electron interaction with optical phonons in the situation when other inelastic electron scattering processes are negligible. The energy oscillations are superimposed on a smooth cooling of the distribution in the transport toward the top of the barrier, as current flows through the system. A comparison with the thermionic theory quantifies the importance of nonequilibrium effects in short-range electronic transport.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A modified Norde function for the measurement of the series resistance and the voltage-dependent barrier height of triangular barrier diodes

The Norde function [J. Appl. Phys. 50, 5052 (1979)] used for measuring the barrier height, series resistance, and ideality factor of a Schottky barrier diode has been modified to obtain the same parameters for a triangular barrier diode (TBD). Unlike Schottky barrier diodes, the barrier height of a TBD depends upon the applied voltage and changes linearly with it. In order to calculate the additive term in the TBD barrier height, the modified function is therefore plotted for both reverse and forward bias cases. It is shown later that the modified Norde function enhances the accuracy of the results.

Control of the barrier height of triangular-barrier diodes by doping their intrinsic layers

An analytic model for the control of the barrier height of a triangular-barrier diode (TBD) is proposed. It is shown that an extra (p- or n-type) doping given to the two intrinsic layers of a TBD changes its barrier height over a wide range (over all 40%). A simple closed-form expression is derived to give the dependence of barrier height on the extra dopings. It is seen that the ideality of the diode is not affected in spite of a wide range of changes obtained in the barrier height. Furthermore, the differential resistance of the device is shown to exponentially decrease with the extra n-type doping given to the structure. Such a strong dependence leads to an improvement in the forward-bias cut-off frequency of the device.

Barrier height enhancement of triangular barrier diodes

A modified model of a triangular barrier diode has been proposed and analyzed by considering the effect of low to moderate p-type doping in the two intrinsic regions. The presence of such acceptor impurities is shown to increase the effective barrier height. The functional dependence of barrier height, saturation current, and ideality factor on various technological parameters is discussed. A method to determine the barrier height and effective Richardson constant has also been suggested. The high-speed switching behavior of this diode is shown to improve.

Silicon triangular barrier diodes by MBE using solid-phase epitaxial regrowth

Triangular barrier diodes have been fabricated in silicon using molecular beam epitaxy (MBE). The extreme profile changes necessary for these devices are realized by growing the desired structure in amorphous silicon layers, which are then crystallized in situ using solid-phase epitaxial regrowth. The resulting diode I-V characteristics compare well with those predicted, and capacitance values are nearly constant, regardless of bias.

Theory of triangular-barrier bulk unipolar diodes including minority-carrier effects

The effect of the minority-carrier charge on the barrier height of the triangular-barrier (TB) majority-carrier diode is considered. The consequences of this effect on the device performance as a diode, transistor, photodetector, and a thyristor is briefly delineated. A two-carrier model of the TB diode is developed to account for this effect. Four other approximate models of the TB diode are compared with the two-carrier model, and the range of their validity established. A high-gain TB "transistor" is proposed based on the mechanism of barrier-height modulation via minority-carrier injection in the TB diode.

Theory of the triangular-barrier switch

The recently observed, current controlled, negative resistance behaviour in a novel bulk GaAs structure is analysed using the basic charge neutrality and carrier transport equations. The structure is composed of a triangular barrier (TB) diode (formed by creating a plane of ionised impurities in the Crystal bulk using MBE) in the immediate vicinity of a p–n junction in the same crystal. The switching phenomena in this ‘TB switch’ is attributed to a regenerative feedback interaction between the p–n junction and the TB diode. Simple closed-form expressions for the main device parameters are derived.

Majority carrier transistor based on voltage-controlled thermionic emission

A new type of transistor is proposed based on gate-controlled charge injection in unipolar semiconductor structures. Its design has some similarity with the recently fabricated triangular barrier diodes but contains an additional input circuit which allows an independent control of the barrier height for thermionic emission. This circuit is provided by a MOS gate on the semiconductor surface. In the proposed device the current flows perpendicular to the semiconductor surface over a planar potential barrier controlled by the gate. The static transconductance characteristics and dynamical response are analyzed. The characteristic response time is limited by the time of flight of electrons across the structure and can be in the picosecond range. The gate voltage required to switch the output current at room temperature is of order 0.2 V.