Schottky barrier height

Table 7. Schottky Barrier Heights for Metals on Compound Semiconductors...

The degree of surface cleanliness or even ordering can be determined by REELS, especially from the intense VEELS signals. The relative intensity of the surface and bulk plasmon peaks is often more sensitive to surface contamination than AES, especially for elements like Al, which have intense plasmon peaks. Semiconductor surfaces often have surface states due to dangling bonds that are unique to each crystal orientation, which have been used in the case of Si and GaAs to follow in situ the formation of metal contacts and to resolve such issues as Fermi-level pinning and its role in Schottky barrier heights. 

The Schottky-Mott theory predicts a current / = (4 7t e m kB2/h3) T2 exp (—e A/kB 7) exp (e n V/kB T)— 1], where e is the electronic charge, m is the effective mass of the carrier, kB is Boltzmann s constant, T is the absolute temperature, n is a filling factor, A is the Schottky barrier height (see Fig. 1), and V is the applied voltage [31]. In Schottky-Mott theory, A should be the difference between the Fermi level of the metal and the conduction band minimum (for an n-type semiconductor-to-metal interface) or the valence band maximum (for a p-type semiconductor-metal interface) [32, 33]. Certain experimentally observed variations of A were for decades ascribed to pinning of states, but can now be attributed to local inhomogeneities of the interface, so the Schottky-Mott theory is secure. The opposite of a Schottky barrier is an ohmic contact, where there is only an added electrical resistance at the junction, typically between two metals. 

The atomic geometry of a surface or interface is, in certain respects, its most fundamental property. Since most surfaces and interfaces are metastable, especially those of technological interest, their composition and structure depends on their process history. Their structures determine, moreover, the "interesting" interfacial properties which are utilized in specific applications, e.g., reactivity and specificity in catalysis or Schottky barrier height in metal-semiconductor contacts. In addition, the interface structure is measurable by one or more of the techniques noted earlier. Therefore the structure of an interface is a measurable link between the process used to prepare it and the electronic and chemical properties which determine its utility. 

Schottky barrier height modulation and stabilization as a "by product" of the original studies. Moreover, since these results are thought to follow from replacement reactions in the vicinity of the interface, they reflect the importance of surface structure as well as composition at semiconductor interfaces. 

The preparation or etching of compound semiconductors is more complex due to the potential of altering the surface stoichiometry. Shiota et al. (36) used AES to show that the final As/Ga at the surface of GaAs was very dependent on the chemical activity of wet chemical etchants. Bertrand was able to follow the changes in the chemical bonding of Ga and As on p-type GaAs etched in HC1 or Br in methanol and relate this to Schottky barrier heights of similarly prepared surfaces with Pb contacts (37). 

Hot electron spin transistors are hybrid metal/semiconductor devices that rely on spin-dependent transport of hot (nonthermalized) electrons rather than electrons near the Fermi level. The spin-valve transistor (SVT) was the first example of this new class of spintronic devices [128, 129], It has a three-terminal structure consisting of a metallic spin-valve base that is sandwiched between two semiconductor substrates, serving as the emitter and the collector, respectively. The electrons in this device are transported perpendicular to the spin-valve layers at energies just above the collector Schottky barrier height. 

Contrary to the MTT the SVT operates at constant hot electron energy that is determined by the collector Schottky barrier height ( 0.8 eV). As a result, the transfer ratio and the MC are only weakly dependent on the emitter/base bias voltage. From Eq. 17 it then follows that the SVT collector current increases almost linearly with the emitter current. It has recently been shown that collector currents exceeding 40 pA and large MC of around 400% can be obtained with SVT devices when large emitter currents are used [156],... 

Fig. 4.1. Example energy band diagrams for a semiconductor/metal contact and and a semiconductor p/n-heterocontact. The Schottky barrier height for electrons B,n is given by the energy difference of the conduction band minimum Ecb and the Fermi energy Ey. The valence and conduction band offsets A/ An and AEcb are given by the discontinuities in the valence band maximum Eyb and the conduction band minimum, respectively...

Photoelectron spectroscopy is a highly surface sensitive technique because of the inelastic mean free path of the photoelectrons Ae, which depends on the electron kinetic energy Ekin and has typical values of 0.2-3nm [31,37,38]. Determination of Schottky barrier heights b, or valence band discontinuities AEyB, can be performed by following the evolution of the position of the valence band maxima with respect to the Fermi level of substrate and overlayer with increasing thickness of the overlayer. For layer-by-layer growth the attenuation of the substrate intensities is given by the inelastic... 

FIGURE 1 Reported Schottky barrier heights of metal contacts to n-GaN [1-19] plotted against the work function of the metal [20],... 

Very little work has been performed on Schottky barrier contacts to the other III-N semiconductors, although a strong dependence of the Schottky barrier height of metal contacts to AIN on the electronegativity of the metal was reported in 1969 [35],... 

Goniakowski J, Noguera C. Electronic states and Schottky barrier height at metal/MgO (100) interfaces. Interface Sci. 2004 12 93-103. 

Fig. 9.6. Measurements of the Schottky barrier height versus metal work function for various metal contacts to a-Si H and crystalline silicon. The dashed line shows the relation for an ideal Schottky contact (Wronski and Carlson 1977).

It is well known that the existence of an insulating layer may have a strong Influence on the diode characteristics and on the determination of the Schottky barrier height, and may give rise to an interface state charge with bias owing to an additional field in the oxide layer. 

As a consequence of Fermi level pinning, the Schottky barrier height < ) =... 

Typical room temperature current-voltage (Z-V) characteristics of Ni/Au SDs are plotted in Figure 6.13. As we can see, the saturation current decreases monotonously with increasing SiN.r deposition time from 0 (the control sample) to 5 min which means that the effective Schottky barrier height increased owing to shallow defect reduction. Meanwhile, the series resistance and ideality factor also decreased when longer SiN deposition times were used. Based on the thermionic emission model, the forward current density at V > 3kT/q has the form [11] ... 

SiN nanonetwork, the barrier height is 0.76 eV. When the SiN deposition time is increased, the barrier height increases from 0.84 (3 min SiN ) to 1.13 eV (5 min SiN (). At the same time, the ideality factor reduces from 1.3 (no SiN ) to 1.06 (5 min SiN ) which indicates that the SDs are nearly ideal in samples grown with the SiN nanonetwork. Incidentally, this improved value is consistent with the work function of Ni (5.2 eV) and the electron affinity of GaN (4.1 eV). In the literature, a value of 1.099 eV (Ni) barrier height was achieved only after the GaN surface was treated with (NH S [12], which is known to passivate the surface defects albeit temporarily. Our results indicate that the Ni Schottky barrier height is very sensitive to the crystalline quality and the excess current... 

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