Thermionic Emission Model Research Articles

Rectification at n-GaAs–n-Ga0.7Al0.3As heterojunctions grown by liquid phase epitaxy

Heterojunctions between n-type GaAs (2×1014cm−3, 1017cm−3) and high purity n-type Ga0.7Al0.3As (∠1×1015cm−3) have been grown by LPE at 700°C, and significant current rectification has been observed across them at room temperature. At low temperatures, the current drops and the degree of rectification increases considerably. The reverse current characteristic shows reasonable semiquantitative agreement with theoretical I–V curves, calculated by using a thermionic emission model. The N–W profile (where N is the concentration and W the depth) measured across the interface indicates qualitatively the presence of a dipolar space–charge region, as expected.

Temperature dependence of the current-voltage characteristics of silicon MIS solar cells

Measurements on the dark I-V characteristics of Al-SiOx- (p-type) Si solar cells as a function of temperature have been used to elucidate one of the possible current conduction mechanisms in MIS solar cells. A good fit is obtained by using the diffusion current mechanism as described previously in our theory of MIS solar cells. There is little evidence in the data on our devices to support the thermionic emission model which is the alternate mode of operation proposed by other investigators.

Carrier transport across heterojunction interfaces

A general theory is presented to describe the carrier transport across heterojunction interfaces. In matching the boundary conditions at the interface, the conservation of total energy and perpendicular momentum is assumed and the difference of effective masses on two sides of the junction is taken into account. The quantum mechanical transmission coefficient is calculated by a combined numerical and WKB method. Application of the present model to an Al xGa 1−xAsGaAs N- n heterojunction is performed and it gives rise to rectifying characteristics together with non-saturated reverse current. Comparison with the classical thermionic emission model is made to show the significance of tunneling and effect of quantum mechanical reflection.

Influence of preparation conditions on forward-bias currents of amorphous silicon Schottky diodes

We report on the open-circuit voltage Voc and the forward-current–voltage characteristic, J=Js(expqV/nKT−1), of Schottky diodes obtained by evaporation of platinum onto hydrogenated amorphous silicon (a-Si :H) fabricated by glow-discharge decomposition of silane. The diode characteristics were studied as a function of several preparation parameters, namely, silane pressure, substrate temperature, silane flow rate, annealing temperature. Rectifying behavior was obtained only for substrate temperatures between 200 and 300°C. Within this constraint, the preparation parameters have only a small effect on Voc but have large influences on n and Js. The factor n decreases towards ideality (n=1) as the silane pressure decreases, as the substrate temperature increases and with annealing of the Pt contact. The corresponding decrease of the concentration of polyhydride H sites with similar variations in the preparation parameters suggests that the recombination center responsible for nonideal value of n are associated with the polyhydride sites. We argue that the nearly constant value of Voc and therefore of the potential barrier probably originates from the crossing of the Fermi level with deep levels near the interface rather than from a previously proposed interface state. Although we were unable to use a sufficiently low temperature to choose between the thermionic emission and diffusion theories for the forward-current-voltage relationship, we point out that carrier injection in the metal base transistor structure favors a thermionic emission model. Assuming thermionic emission the value deduced for the Richardson constant is of the same order of magnitude as found for crystal Si Schottky barriers.

Photodetection by light-induced barrier modulation in Cu-diffused Au–CdS diodes

Modified Schottky barriers of the type Au–CdS : Cu were prepared by diffusing Cu to a depth of 0.1–0.2 μm into single crystals of CdS, prior to evaporating rectifying Au contacts. The electronic and photoelectronic properties of these junctions are adequately described by a simple model in which the Cu acts as an ionized acceptor, resulting in a ``humped'' potential barrier between the Au and the bulk CdS. Hole trapping by the acceptors under band-gap illumination reduces their ionization and, consequently, the hump height. The forward current density in the dark and under illumination can be accurately described by a thermionic emission model as J=A*T2 exp {—e[VB+VH(0)]/kT exp}(eV/βkT), where the hump potential VH (0) is light sensitive and where β (1<β<1.35) arises from a weak voltage dependence of the barrier height. Barrier height determinations, in the dark and under illumination with 5000-Å light, by means of internal photoemission, thermal activation energy, and J-V measurements unequivocally show that under saturating light conditions the hump in the potential barrier is reduced by 0.23±0.03 V. This barrier mechanism of photoconductive response results in steady-state electron/photon gains in excess of 106 at light intensities lower that 5×1011 photons cm−2 sec−1, where response times exceed 1 sec.

Electrical Properties of a Native Oxide on Gallium Phosphide

A vitreous native oxide can be grown on by oxidation in a concentrated solution of hydrogen peroxide, and this oxide effectively passivates light‐emitting devices. This paper reports the first electrical characterization of this native oxide. Electrical measurements were performed on MOS structures prepared by growing a native oxide film 500–1000AÅ thick on the face of an n‐ or p‐type wafer and evaporating an Au field plate on the oxide. The refractive index of the oxide film was 1.58. Current‐voltage and capacitance‐voltage characteristics show that the native oxide is an electrical insulator, with a low frequency dielectric constant , and a dielectric breakdown strength of after annealing in nitrogen at 250°C. Current‐voltage behavior shows a linear dependence of In , typical of field‐enhanced thermionic emission. The characteristics are nonsymmetric with respect to field plate polarity, suggesting the conduction mechanism to be surface‐barrier‐controlled emission, with a barrier height , as determined from the temperature dependence of the characteristics. The dielectric constant determined from the slope of the characteristics by using a field‐enhanced thermionic emission model agrees with the value obtained from capacitance measurements. Capacitance‐voltage characteristics show accumulation and deep depletion behavior. Analysis of deep depletion curves yields a surface charge density for both p‐ and n‐type samples. Values of for the substrates obtained from deep depletion data are in good agreement with the values obtained from Hall measurements on the substrate material.

Effects of humidity and organic coating on surface potential propagation in passivated devices : T. A. Temofonte and J. R. Szedon. Proc. IEEE Reliab. Phys. Symp., Las Vegas, USA. 31 March–2 April (1971)

We investigated the electron injection process for high-speed N-p-n AlInAs/GaInAs HBTs by measuring collector and base currents as a function of base-emitter voltage with collector-base voltage equal to zero (Gummel plots) at temperatures from 77 to 300 K. We compared the measured collector current with calculations based on electron injection from emitter to base by tunneling through the conduction band spike and thermionic emission over it, using a modified version of the thermionic-field emission theory developed by Crowell and Rideout. Good agreement was obtained between the experimental collector current ideality factor and tunneling-thermionic emission theory for all temperatures and currents. This is an improvement over drift-diffusion and thermionic emission models, which have been used for HBTs but which do not correctly describe the experimentally observed temperature and current dependence of the ideality of the collector current. The tunneling-thermionic emission model explains the increase in collector current ideality factor that occurs as the transistor is biased at high collector current density (JC ≧ 105Acm−2), which is the regime of operation in which fT is maximized and a low ideality factor is most important. The model also explains the experimentally observed variation of hFE with ln IC. Thus the tunneling-thermionic emission model is a useful aid in the design of the epitaxial structure for high-frequency HBTs.

Formation of NiSi and current transport across the NiSi-Si interface

The metallic compound NiSi has been produced by solid-solid metallurgical reaction in both n- and p-type silicon by sputtering Ni onto freshly back-sputtered silicon wafers and sintering for 5 min at 550°C. Identification of the orthorhombic (B31) monosilicide phase was made by X-ray diffraction, utilizing a glancing-angle Debye-Scherrer photograph of the 1300 Å thin-film phase on the silicon substrate. NiSi Schottky barrier diodes, formed by this technique through holes in a silica mask and containing diffused guard rings around the periphery of the metallization, yield nearly ideal reverse I– V characteristics. The data have been fitted to a thermionic emission model for current transport, with barrier heights of 0.66 and 0.45 (eV) to n- and p-type silicon, respectively. The nature of the current transport characteristics strongly indicates the presence of a dipolar charge layer at the metal-semiconductor interface caused by quantum mechanical penetration of metallic electrons into the forbidden gap of the semiconductor.

Electronic Conduction Through Single Crystals of Polyethylene

Current densities of the order of 10−8 A/cm2 at field strengths of 3×106 V/cm have been measured for electrical conduction through single-layered polyethylene crystal samples at room temperature. The dependence of current density on field strength has been fitted to the Richardson-Schottky model of field-assisted thermionic emission.

Characteristics of aluminum-silicon schottky barrier diode

AbstractAluminumn-type silicon Schottky barrier diodes with near-ideal characteristics have recently been developed. In this paper the characteristics of such a Schottky barrier are discussed. The IȁV characteristics agree well with the theoretical thermionic emission model. The barrier height is determined from the saturation current, temperature dependence of forward current, and photoemission to be0.69±0.01eV. The switching measurements show no minority carrier storage, as expected. The low-frequency noise is very low and is comparable to the bestp-n junction and guard-ring Schottky barrier. These desirable features, coupled with the simple process of the Al-nSi Schottky barrier, make them attractive in a variety of applications.