Resonant-tunneling diode

Characteristic to the current–voltage relationship of a tunneling diode is the presence of one or more negative differential resistance regions, which enables many unique applications.

The structure and fabrication process of Si/SiGe resonant interband tunneling diodes are suitable for integration with modern Si complementary metal–oxide–semiconductor (CMOS) and Si/SiGe heterojunction bipolar technology.

One type of RTDs is formed as a single quantum well structure surrounded by very thin layer barriers.

When a voltage is placed across an RTD, a terahertz wave is emitted, which is why the energy value inside the quantum well is equal to that of the emitter side.

Considering a potential profile which contains two barriers (which are located close to each other), one can calculate the transmission coefficient (as a function of the incoming particle energy) using any of the standard methods.

Tunneling through a double barrier was first solved in the Wentzel-Kramers-Brillouin (WKB) approximation by David Bohm in 1951, who pointed out the resonances in the transmission coefficient occur at certain incident electron energies.

Later, in 1964, L. V. Iogansen discussed the possibility of resonant transmission of an electron through double barriers formed in semiconductor crystals.

Advances in the MBE technique led to observation of negative differential conductance (NDC) at terahertz frequencies, as reported by Sollner et al. in the early 1980s.

Such devices have not entered mainstream applications yet because the processing of III-V materials is incompatible with Si CMOS technology and the cost is high.

[9][10] Recently, the device-to-device variability in an RTDs current–voltage characteristic has been used as a way to uniquely identify electronic devices, in what is known as a quantum confinement physical unclonable function (QC-PUF).

[13] Resonant tunneling of electrons through Si/SiGe heterojunctions was obtained later, with a limited peak-to-valley current ratio (PVCR) of 1.2 at room temperature.

[22] The five key points to the design are: (i) an intrinsic tunneling barrier, (ii) delta-doped injectors, (iii) offset of the delta-doping planes from the heterojunction interfaces, (iv) low temperature molecular beam epitaxial growth (LTMBE), and (v) postgrowth rapid thermal annealing (RTA) for activation of dopants and reduction of density of point defects.

[27] Vertical integration of Si/SiGe RITD and SiGe heterojunction bipolar transistors was also demonstrated, realizing a 3-terminal negative differential resistance circuit element with adjustable peak-to-valley current ratio.