MIS Tunnel Diodes Research Articles

Dark-capacitance transients in MIS tunnel diodes

Dark-capacitance transients in MIS tunnel diodes switched from accumulation to deep depletion depend on the interface state occupancy. This time dependent function is derived and its behavior described for electron emission and electron-hole pair generation with tunneling and thermally controlled occupancies. A new method of determining the tunneling relaxation time constant τ T from the electron emission transient at low temperature is described. Measurements of MIS tunnel diodes with oxide thickness d ox = 17 to 80 Å agree with theory and the resultant values of τ T compare with previously reported results from photocapacitance[2].

Heterogeneous distribution of interstitial oxygen in annealed Czochralski-grown silicon crystals : Fumio Shimura, Yoshitake Ohnishi and Hideki Tsuya. Appl. Phys. Lett.38 (11), 867 (1981)

Noise of MIS tunnel diodes is investigated theoretically; both majority carrier and minority carrier contributions are taken into account, starting from the small signal equivalent circuit of the structure. In particular it is shown that, when it is difficult for minority carriers to cross the insulator, they can induce in the majority carrier current a very large low-frequency modulation noise of the generation-recombination (g-r) type.

New method for the determination of the surface barrier heights in MIS tunnel diodes (solar cells)

The methods commonly applied for the determination of the surface barrier heights of Schottky diodes are usually extended for the MIS tunnel structures characterization, although, in such cases both, their range of application and accuracy are often strongly reduced. In this paper a new photoelectric method for the determination of the surface barrier heights in MIS tunnel diode is proposed together with experimental results supporting its validity. The presence of the ultra-thin oxide layer between the metal and semiconductor does not reduce method's applicability as long as the direct semiconductor-metal tunneling is dominant current flow mechanism through the oxide layer. In the contrary to the previous methods it allow us to measure directly the barrier height for minority carriers, and therefore, is especially recommended for minority carrier dievices.

Bulk and surface states analysis in a-Si:H by Schottky and MIS tunnel diodes capacitance and conductance measurements

An experimental and theoretical study of both the capacitance and the conductance of Schottky and MIS tunnel diodes made on undoped a-SI:H, versus frequency, temperature, and voltage is presented in this paper. It is based on a general model using an equivalent electrical circuit of the devices, which permits an unambiguous distinction to be made between the contributions of bulk surface states, to determine their respective densities and to analyze their kinetic properties, It is shown that the bulk density of states (DOS) can be determined from capacitance and conductance measurements versus temperature and frequency on both Schottky and MIS devices, provided the modulation frequency is high enough to prevent any contribution from surface states. It is demonstrated that capacitance-voltage characteristics of Schottky diodes cannot provide reliable information about either bulk or surface as the diffusion theory and not the thermionic theory is appropriate to describe the transport of electrons across the junction. It is shown theoretically and experimentally that a MIS device is required to measure surface states, the insulator preventing the screening of their contribution by the metal. The measured surface DOS, derived by three different and independent methods, is very high (5×1012−2×1013 cm−2 eV−1) and essentially the same for all the investigated samples whose bulk DOS around the Fermi level ranges between 5×1015 and 4×1017 cm−3 eV−1. From conductance measurements, it is shown that the kinetics of the occupancy of both bulk and surface states is controlled by free electron transport in the conduction band and not by the states’ interaction kinetics with these electrons. The very high derived lower limit of the effective capture cross section sn of electrons by states around the Fermi level EF(sn ≳5×10{13 cm2) implies either that the interaction between states around EF and free electrons takes place via intermediate states of that the actual distance between the bulk Fermi level and the conduction level is smaller than the activation energy Es of the conductivity.

A chemically sensitive MOS element with an ultra thin dielectric film

The use of an MIS tunnel diode with an ultrathin SiO 2 film as a humidity and hydrogen ion sensor is described in this paper.

Effect of minority carrier injection on lateral current in MIS tunnel structures

In this work it is shown that the MIS structure with an ultra-thin (20 A ̊ < x i < 40 A ̊ ) oxide is distinguished by a unique mechanism of lateral conduction. The flow of the lateral current between the two metal electrodes formed on the surface of an ultra-thin silicon dioxide is found to take place through the silicon substrate and the two non-equilibrium MIS tunnel diodes formed by the metal electrodes, the ultra-thin oxide, and the silicon. One of these diodes is forward biased and the other reverse biased. It is shown that the main limitation to the lateral current comes from the reverse biased diode. A structure is proposed in which such a lateral current can be efficiently controlled by the injection of minority carriers from the gate of an appropriately formed, conventional MIS tunnel diode into the depletion region of the reverse biased diode, so limiting the lateral current. Various physical phenomena related to this effect are studied and discussed. The MIS lateral tunnel structure considered in this work was fabricated in order to investigate the influence of minority carrier injection on the lateral conduction in MIS tunnel devices. However, the ideas proposed in this work can be developed into useful device structures.

The potential barrier height of minority-carrier MIS tunnel diodes

Expressions for the potential barrier height of minority-carrier MIS tunnel diodes both at thermal equilibrium and in the presence of applied voltages are derived and solved numerically. The derived expressions are based on a model that takes into account the presence of the inversion layer at the semiconductor surface. The limitations of previous treatments are pointed out.

Statistics of trap photoemission in MIS tunnel diodes

The occupancy rate equation is solved for bulk and interface states in MIS tunnel diodes under chopped illumination of photon energy ifhv < Eing. The occupancy function f( t) oscillates with the chopping frequency ω around an average occupancy, which itself decays exponentially with relaxation time τ from an initial occupancy f 0 at t = 0 to the steady state occupancy f u at time t ⪢ τ. The photocurrent induced in the external circuit has the amplitude I( t) = I sat + I dec ( t). The first component I sat is the saturation value which I( t) approaches for t ⪢ τ. The second I dec ( t) of decaying amplitude is observed when the average state occupancy relaxes from f 0to f u . This is equivalent to the depopulation processes observed in ⋍ 1000 A ̊ MOS structures by previous workers using steady illumination. Finally, it is shown how the state distribution and the photoionization cross section can be obtained from the measured temperature and time dependence of the photocurrent amplitude I( t).

Minority carrier induced modulation noise in MIS tunnel diodes

Noise of MIS tunnel diodes is investigated theoretically; both majority carrier and minority carrier contributions are taken into account, starting from the small signal equivalent circuit of the structure. In particular it is shown that, when it is difficult for minority carriers to cross the insulator, they can induce in the majority carrier current a very large low-frequency modulation noise of the generation-recombination ( g- r) type.

Measurement of Minority Carrier Lifetime and Impurity Concentration in Epitaxial Silicon Using MIS Tunnel Diodes

Measurement of Minority Carrier Lifetime and Impurity Concentration in Epitaxial Silicon Using MIS Tunnel Diodes

New TiOx-MIS and Si02-MIS silicon solar cells

Two new types of solar cells are described in which either a TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> or a SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> layer is deposited onto p silicon; contacts are obtained by means of a MIS tunnel diode grid. It is shown that the TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> -MIS cells can be realized by single-mask completely low-temperature processing by employing spin-on of titanium-oxide antireflective coating. Conversion efficiencies of 8 percent at AM1 have been achieved with these cells; they perform even more efficiently at higher illumination levels. With the SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> -MIS cells efficiencies of 12 percent have been reached, at the expense of a slightly more complicated process. A detailed comparison between the two cells is given.

Theory of metal-insulator-semiconductor solar cells

Recent reports in the literature indicate that the introduction of an interfacial oxide layer in a Schottky barrier can greatly increase the photovoltaic conversion efficiency of such devices. We propose an explanation for the operation of such solar cells based on the concept that they are minority-carrier nonequilibrium MIS tunnel diodes. Calculations of efficiency as a function of insulator thickness, substrate carrier concentration, surfaces states, and oxide charge are presented. These indicate that a maximum theoretical efficiency of 21% is possible under AM2 illumination for high substrate doping and low interface defect density.

Tunnel MIS solar cells

In a recent publication we have proposed an explanation for the operation of Schottky‐barrier solar cells with an interfacial oxide layer based on the concept that they are minority‐carrier nonequilibrium MIS tunnel diodes. Such devices represent a potentially low‐cost method for fabricating large‐scale solar‐energy‐conversion arrays both with single crystals and polycrystalline film semiconductors. These solar cells are identical to the conventional p–n junction device except for the location of the depletion region. Our calculations indicate that one would have to grow defect‐free ultra‐thin (10–15 Å in the case of Al–SiO2–Si structure) interfacial oxide layers to get highest conversion efficiencies from these devices. Performance of tunnel MIS solar cells will be described with main emphasis on the role of surface states and oxide charges.

Photovoltaic effect in MIS diodes or Schottky diodes with an interfacial layer

Recent reports in the literature indicate that the introduction of an interfacial oxide layer in a Schottky barrier can increase greatly the photovolatic conversion efficiency of such devices. We propose an explanation for the operation of such solar cells based on the concept that they are minority-carrier nonequilibrium MIS tunnel diodes.

Determination of minority carrier lifetime using MIS tunnel diodes

A new and simple method that employs MIS tunnel diodes is described here for the determination of minority carrier lifetime in semiconductors. For large reverse bias, a direct current was measured across Si–SiO2-metal devices with oxide thickness between 40 and 60 Å. This current is the generation current in the semiconductor space-charge layer, and the lifetime is easily obtained from it.

Equilibrium-to-nonequilibrium transition in MOS (surface oxide) tunnel diode

When the insulator barrier in a tunneling MIS diode is less than a certain critical thickness (approximately 30 Å for Al–SiO2–Si at 300 °K), the semiconductor departs from thermal equilibrium and a new type of ``nonequilibrium'' current-voltage characteristic results. Such nonequilibrium diodes have been found to possses current multiplication properties and have been used as the basis of the tunnel surface oxide transistor (SOT) reported by Shewchun and Clarke. They have also been applied to direct energy conversion employing the electron-voltaic and photovoltaic effects. The transition of the MIS tunnel diode from the equilibrium to this nonequilibrium mode is investigated as a function of insulator thickness, metal work function, and temperature as well as a number of semiconductor parameters. A nomograph is presented to assist in determining when the MIS tunnel diode is in the nonequilibrium mode. Surface-state tunneling is seen to play an important role in determining part of the nonequilibrium current-voltage characteristic.

Small Signal Equivalent Circuit for an MIS Tunnel Diode

A.C. components of small signal of tunneling currents and recombination current are deduced for an MIS tunnel diode with a very thin insulating film. The equivalent circuit is presented. The derivation is based on Freeman and Dahlke's theory.10) Our equivalent circuit, however, contains no active element. Three types of interface-state distributions are assumed; a single level, uniform and double-peak distributions. Each element in the equivalent circuit is computed for each distribution and for various insulator thicknesses as a function of the applied voltage. The measured conductance and capacitance are compared with the calculations. A qualitative agreement is found to be satisfactory with the result based on the uniform distribution.