Schottky Barrier Height Measurements Research Articles

Structure and growth kinetics of RhSi on single crystal, polycrystalline, and amorphous silicon substrates

Growth kinetics of rhodium silicide in the temperature range of 375–450 °C have been studied on three different silicon substrates: single crystal, polycrystalline, and amorphous. The methods of analysis and specimen characterization utilized in this study are Rutherford backscattering spectroscopy (RBS), Seemann–Bohlin x-ray diffraction, cross-sectional transmission electron microscopy (TEM), sheet resistivity via four-point probe, and Schottky barrier height measurements obtained from the current-voltage relationship. Our results conclude that all three silicon substrates form an identical rhodium silicide compound, RhSi, indicating that the crystallinity of the substrate has no effect on the resulting rhodium silicide. The growth of RhSi was determined to be diffusion-limited and the activation energy of growth was similar for single crystal (1.88±0.04 eV) and amorphous silicon (1.86±0.07 eV), yet it was slightly lower (1.71±0.08 eV) for polycrystalline silicon. The difference can be attributed to the rhodium silicide compound having a smaller grain size in the polycrystalline silicon case. The layer formation and the thickness of rhodium silicide between unreacted rhodium and the three different silicon structures was examined by cross-sectional TEM and compared to those measured by RBS.

TiN as a diffusion barrier between CoSi2 or PtSi and aluminum

The effectiveness of a thin (360 Å) layer of reactively sputtered TiN as a diffusion barrier between aluminum and two silicides (PtSi and CoSi2) was evaluated. The chemical composition, structural phases and electrical properties of silicide/Al and silicide/TiN/Al contacts to n-type silicon were studied by Rutherford backscattering spectroscopy, glancing angle X-ray diffraction and Schottky barrier height measurements respectively. The results show that TiN is an effective barrier in these two systems up to at least 450 °C, the typical temperature at which aluminum contactsv are sintered.

Photoemission studies of the Au–InP(110) interface

We report new photoemission studies of the Au–InP (110) interface for both n- and p-type samples using synchrotron radiation in the energy range 80 to185 eV. By slowly increasing Au coverages and by studying core level structures and valence band spectra we have been able to differentiate between two coverage intervals. The lower coverage interval (θ<1 ML) is dominated by band bending with no measurable chemical changes and with a total measured Schottky barrier height of 0.6 eV. In the higher coverage interval (1<θ≤37 ML), we observed changes in the In 4d and P 2p core level shapes and a monotonic shift of the Au 4f to lower binding energies with increased Au coverage. Evidence of intermixing of Au with the P and In atoms indicates the formation of a nonabrupt interface. These results are at variance with the view that Au is a nonreactive metal on InP (110).

A study of vanadium as diffusion barrier between aluminum and gadolinium silicide contacts

Implementation of GdSi2 as low-barrier (0.4 eV) Schottky contacts in a Si device requires a diffusion barrier between the GdSi2 and Al interconnects to prevent Al penetration. In this work, the effectiveness of vanadium films as such a diffusion barrier has been studied by using a set of complimentary experimental techniques: nuclear backscattering, x-ray diffraction, and current-voltage measurement of Schottky barrier height on both n-type and p-type Si substrates. We found that the effectiveness depends strongly on how the thin-film structure of Al/V/GdSi2/Si was made, and especially on the formation process of GdSi2. The GdSi2, which was formed upon deposition onto a high-temperature substrate, is superior in stability by showing no Al penetration to other processing schemes investigated. These results are explained by structural and compositional changes occurring in the layered films of Al/V/Gd/Si as a function of heat treatment. In order to understand the complex interdiffusion and compound formation in the layered structure, the reactions between neighboring layers have been studied: Al interacts with V at ∼450 °C, forming Al3V and possibly Al10V; V does not react with Gd, even at 700 °C; and Gd is known to react with Si to form GdSi2 at∼350 °C. On the other hand, Al reacts readily with Gd at 250 °C to form a metastable compound of Al4Gd, which then transforms to Al3Gd at 400 °C, and the formation of these compounds has been found to retard the reaction between Gd and Si.

Formation and Schottky behavior of manganese silicides on n-type silicon

The formation of manganese silicides on Si has been studied by using Rutherford backscattering spectroscopy and glancing-incidence x-ray diffraction; electrical properties of these silicides on n-Si have been studied by current-voltage measurement of Schottky barrier height and four-probe measurement of sheet resistivity. Two silicides have been identified: MnSi formed at 400 °C and MnSi1.7 at 500 °C. The former obeys a parabolic growth in layer form with an activation energy of 1.9 eV, yet the latter grows in patches and is governed by a linear growth. The values of Schottky barrier height on n-type Si of these two silicides are very close: 0.65 and 0.67 eV, respectively, but their sheet resistivities differ significantly: 220 μΩ cm for MnSi and 4100 μΩ cm for MnSi1.7.

Role of cation dissociation in Schottky barrier formation at II–VI compound semiconductor-metal interfaces

We used UV and X-ray photoemission spectroscopies to probe the relation between the chemical and electronic structure at ultrahigh-vacuum-cleaved CdS-metal and CdSe-metal interfaces. When combined with current-voltage and capacitance-voltage studies of the same interfaces in ultrahigh vacuum, the experimental results indicate that partially dissociated cadmium cations, produced as a consequence of interfacial chemical reaction, may be the electrically active species giving rise to the observed Fermi level stabilization at these contacts. The extent of cation dissociation, a spectroscopically determined quantity, is shown to correlate inversely with the measured Schottky barrier height. An indirect and modified doping effect is suggested as one possible mechanism to explain this behavior. Features of interdiffusion, in particular regarding the interfacial distribution of dissociated cadmium, are also described.

Schottky barrier height measurement by electron-beam induced voltage

We demonstrate that electron-beam induced voltage (EBIV) technique can be used for direct measurement of Schottky (or p-n junction) barrier height. Schottky barrier heights of PtSi, Pd2Si, and TiSi2 on n-type (111) Si measured by this technique were found to be 0.84, 0.74, and 0.57 eV, respectively, in excellent agreement with values obtained by the standard current-voltage technique. Because of no complication due to leakage current in EBIV measurement, this technique is particularly suited for studying the formation of low barrier height Schottky diodes. Furthermore, this technique can be extended for in situ measurements of barrier height to supplement surface electron spectroscopy studies on the electrical and chemical characteristics of silicide/Si interfaces.

Refractory metal contacts to GaAs: Interface chemistry and Schottky-barrier formation

A survey of the interface chemistry of the refractory metals W, Ta, Re, Ir, and Mo during room- temperature Schottky-barrier contact formation to GaAs by using x-ray photoemission spectroscopy (XPS) is reported. The metals were deposited onto clean n-type GaAs (100) surfaces within the XPS system by two methods: Evaporation and plasma sputtering. For each metal a distinct interfacial reaction which produced GaAs dissociation and formation of a new metal arsenide is observed. Refractory metals are in general not chemically inert in contact to GaAs and nonabrupt interfaces ∠10 Å in width are formed. XPS was also used to correlate interface chemistry with measurement of Schottky-barrier height during contact formation. XPS measured barrier heights ranged from 0.9–0.7 eV, in the order W, Ir, Mo, Ta, and Re.

HgTe/CdTe heterojunctions: A lattice-matched Schottky barrier structure

HgTe-CdTe lattice-matched heterojunctions were formed by the epitaxial growth of HgTe on CdTe substrates using a low-temperature metal organic chemical vapor deposition technique. These heterojunctions combine features of the Schottky barrier structure, due to the high carrier concentrations found in the semimetallic HgTe, with the structural perfection present in a lattice-matched heterojunction. The measured Schottky barrier height varied from 0.65 to 0.92 eV depending on the details of the heterojunction growth procedure used. This dependence may be due to the formation of an inversion layer in the CdTe at the interface. Presence of such an inversion layer suggests that the valence band discontinuity between HgTe and CdTe is small, in agreement with previous theoretical estimates.

Tin as a Diffusion Barrier Between CoSi2 or PtSi and Aluminum

The effectiveness of a thin (360Å) layer of reactively sputtered TiN as a diffusion barrier between aluminum and two silicides (PtSi and CoSi2) was evaluated. The chemical composition, structural phases and electrical properties of silicide/Al and silicide/TiN/Al contacts to n-type silicon were studied by Rutherford backscattering spectroscopy, glancing angle X-ray diffraction and Schottky barrier height measurements respectively. The results show that TiN is an effective barrier in these two systems up to at least 450°C, the typical temperature at which aluminum contacts are sintered.

Formation of shallow Schottky contacts to Si using Pt-Si and Pd-Si alloy films

A series of codeposited alloy films of Pt-Si with a composition changing from Pt75Si25 to Pt50Si50 and of Pd-Si changing from Pd75Si25 to Pd67Si33 have been prepared on Si for a systematic study of shallow silicide contacts. The effects of alloy composition and heat treatment on the formation and properties of these contacts have been investigated by I-V measurement of Schottky barrier height, glancing incidence x-ray diffraction, and cross-sectional transmission electron microscopy. Shallow contacts with a depth of about 10 nm and with the Schottky barrier height of PtSi and Pd2Si have been achieved.

Role of Cation Dissociation in Schottky Barrier Formation at II–VI Compound Semiconductor-Metal Interfaces

We used UV and X-ray photoemission spectroscopies to probe the relation between the chemical and electronic structure at ultrahigh-vacuum-cleaved CdS-metal and CdSe-metal interfaces. When combined with current-voltage and capacitance-voltage studies of the same interfaces in ultrahigh vacuum, the experimental results indicate that partially dissociated cadmium cations, produced as a consequence of interfacial chemical reaction, may be the electrically active species giving rise to the observed Fermi level stabilization at these contacts. The extent of cation dissociation, a spectroscopically determined quantity, is shown to correlate inversely with the measured Schottky barrier height. An indirect and modified doping effect is suggested as one possible mechanism to explain this behavior. Features of interdiffusion, in particular regarding the interfacial distribution of dissociated cadmium, are also described.

Schottky barriers on diamond (1 1 1)

We have measured Schottky barrier heights Ø B = 1.3 eV for Au and Ø B = 1.5 eV for Al on ( p-type) diamond(1 1 1)−(1 × 1) using photoelectron spectroscopy with synchroton radiation. These barrier heights yield a barrier index of S = 0.2, which is closer to the values for Si and Ge ( S ∼ 0.1) than to the value S = 0.4 calculated for jellium on an ideal diamond(1 1 1) surface. After reacting Al with the diamond surface by annealing to 800° C, we find that Ø B decreases by 0.24 to 1.25 eV.

Effect of substrate temperature on the formation of shallow silicide contacts on Si using Pd-W and Pt-W alloys

We have investigated the effect of substrate temperature on the reaction between Si and Pd-W and Pt-W alloys by I-V measurement of Schottky barrier height. We found that by maintaining a substrate temperature of 100 °C during the deposition of W-rich Pd20W80 alloys, Schottky contacts of Pd2Si on Si can be obtained without any subsequent annealing. Similarly, a substrate temperature of 300 °C enables the formation of PtSi during the depostion of W-rich Pt20W80 alloys. For Pd-rich Pd80W20 and Pt-rich Pt80W20 alloys, the substrate-temperature effect is not as significant as for the W-rich alloys.

Contact reaction between Si and Pd-W alloy films

Contact reactions in the temperature range 250–650 °C between (100) Si and Pd-W binary alloy films of composition Pd80W20 and Pd30W70 have been studied by a combination of ion backscattering, x-ray diffraction, and current-voltage measurement of Schottky barrier height. For the Pd-rich alloy, the reaction around 400 °C produced the silicide Pd2Si by depleting Pd from the alloy and resulted in the formation of a two-layer structure, W/Pd2Si/Si. We have found that the W layer has served effectively as a diffusion barrier for the subsequently deposited Al, indicating that a rectifying contact and its diffusion barrier can be fabricated simultaneously. At higher reaction temperatures, the W layer transforms to WSi2 with some mixture of Pd2Si. The alloying of Pd with W has been found to increase the formation temperature of Pd2Si but decrease that of WSi2. In the Pd80W20 reaction, Pd2Si forms around 400 °C and WSi2 around 500 °C. In the Pd30W70 reaction, Pd2Si forms around 500 °C and WSi2 around 650 °C.

A study of interface problems in polycrystalline GaAs Schotky barrier and MIS solar cells

AbstractAES, SIMS and XPS are used to investigate the interfaces in polycrystalline GaAs Schottky barrier and MIS solar cells. A significant interfacial chemical reaction is found to occur between Au and the GaAs in room temperature fabricated devices, with at least one phase, Ga2Au, identified using chemical peak shifts in XPS. Enhanced interdiffusion is reported at elevated temperatures for these structures. The primary mechanism is identified to be grain boundary diffusion, and the temperature dependence of the diffusion coefficient is estimated from the AES depth‐compositional data. The interface in the Ag/GaAs Schottky barrier is studied for comparison and is found to be stable to 573 K. The measured Schottky barrier heights and photovoltaic performances of these solar cells are correlated with the condition of the metal‐semiconductor interface. The advantage of including a thin oxide layer between the Au and GaAs (MIS structure) in preserving the integrity of the interfaces is demonstrated.

Correlation of the Schottky barrier height measurements determined from the capacitance method and the saturation current

Correlation of the Schottky barrier height measurements determined from the capacitance method and the saturation current