P-type Surface Research Articles

A note on TiN/Si (1 0 0) contacts

The contact properties of TiN on p- and n-type Si (1 0 0) obtained by magnetron reactive sputtering were investigated. Schottky diode characteristics were observed on p-type Si (1 0 0) as determined by forward current–voltage ( I– V) measurements, but on n-type Si (1 0 0) the reverse I– V relation has shown a nonsymmetrical character. The zero-bias barrier heights evaluated by I– V on both type diodes were in the range of ∼0.60–0.64 V within the range of a few mVs, not more than ∼±(10–30) mV from each other. Incorporation of the effect of the series resistance in the I– V analysis resulted in a significant reduction in the magnitude of the ideality factor of the TiN/p-type specimen. Almost no change has occurred in the barrier height values. The contradictory reports on the TiN/n-type Si (1 0 0) diode characteristics in earlier works have been explained in terms of surface passivation of Si by the HF cleaning solution. It was stated in these reports that following annealing at 673 K the diodes have shown rectifying behavior. It has been speculated, that the nonsymmetrical nature of the TiN/n-Si (1 0 0) showing an intermediate behavior between Ohmic and rectifying behavior is a result of the specimen being exposed to a temperature lower than 673 K during sputtering where no complete depassivation took place. In order to obtain a rectifying behavior of TiN on both n-type and p-type Si surface passivation has to be eliminated.

Dependence of Oxidative Gas Reaction on Diamond p-Type Surface Conductive Layer Annealed with Hydrogen Gas

To develop the gas sensing devices using diamond films, time dependence of the surface resistance on the diamond film surrounded by oxidative gas has been investigated. After the termination of the diamond films surface by oxygen atom, the samples were annealed by hydrogen gas from 10 to 90 minutes (by 10 minutes step) under 900°C. The time depending changes in the surface resistance were measured in NO2 gas and N2 gas atmospheres. Following results were obtained. That is, in NO2 gas atmosphere, transient time response of surface resistance of respectively annealed samples showed the almost identical time dependences. On the other hand, in N2 gas atmosphere, samples were indicated no remarkable changes in annealing effect. To seek the situation concerned with the termination of annealed samples, the surface hydrogen densities per unit area were measured by ERDA (Elastic Recoil Detection Analysis). From these results, change mechanism of surface resistance due to annealing effect by hydrogen gas was discussed qualitatively.

Recovery of negative electron affinity by annealing on (111) oxidized diamond surfaces

We discovered that oxidised (111) p-type boron-doped homoepitaxial diamond film surfaces grown by chemical vapor deposition (CVD) recover negative electron affinity (NEA) after annealing the samples in vacuum or under an Ar atmosphere. On the other hand, (001) p-type boron-doped homoepitaxial CVD diamond surfaces do not show NEA recovery. The oxidised (111) surface possesses positive electron affinity of + 0.6 eV, whereas the subsequently annealed surface has a negative electron affinity of − 0.8 eV, indicating a partial hydrogen termination condition that is supported by XPS results. These distinct behaviours should be taken into consideration for investigating the surface electronic properties of diamond.

Numerical Evaluation of Forward Voltage in SiC Pin Diode with Non-Ohmic Current Component in Contact to p-Type Layer

Forward voltage of SiC pin diodes is evaluated by device simulation, where a p-type contact is described by Schottky barrier to a p-type surface region. The contact resistance is calculated from the comparison to I-V characteristic of Schottky structure to a p-SiC layer with a sufficiently low Schottky barrier height. Even in the relatively low contact resistance rc of 10-4 Wcm2, non-ohmic current component is observed in Schottky structure to p-SiC and the increase of forward voltage of pin diodes is fairly small. Forward voltage of pin diodes increases in the pin diodes with contact resistance rc over 10-4 Wcm2. The same behavior is also observed irrespective of a time constant of carriers, and doping concentration and thickness of a drift layer.

Electron microscopy analysis of crystalline silicon islands formed on screen-printed aluminum-doped p-type silicon surfaces

The origin of a not yet understood concentration peak, which is generally measured at the surface of aluminum-doped p+ regions produced in a conventional screen-printing process is investigated. Our findings provide clear experimental evidence that the concentration peak is due to the microscopic structures formed at the silicon surface during the firing process. To characterize the microscopic nature of the islands (lateral dimensions of 1–3 μm) and line networks of self-assembled nanostructures (lateral dimension of ≤50 nm), transmission electron microscopy, scanning electron microscopy, scanning transmission electron microscopy, and energy dispersive x-ray analysis are combined. Aluminum inclusions are detected 50 nm below the surface of the islands and crystalline aluminum precipitates of ≤7 nm in diameter are found within the bulk of the islands. In addition, aluminum inclusions (lateral dimension of ∼30 nm) are found within the bulk of the self-assembled line networks.

Investigations of hydrogen sensors made of porous silicon

Porous silicon layer was formed by electrochemical anodization on n- and p-type silicon surface. Thereafter n-type TiO 1.98 and ZnO〈Al〉 thin films were deposited onto porous silicon surface by electron-beam evaporation and magnetron sputtering, respectively. A Pt catalytic layer and Au electrical contacts for further electrical measurements were deposited by ion-beam sputtering. Changes in sensitivity versus time of obtained structures were examined for different concentrations of hydrogen gas and propane–butane mixture. High sensitivity and selectivity to hydrogen gas was detected. All measurements were carried out at 40 °C.

Evaluation of implanted InSb p+n diodes passivated with composite anodic oxide/SiOxstack

This investigation presents detailed characteristics of an implanted planar InSb p+n diode with a junction area scaled down to 20 × 20 μm2. Low-temperature photo-chemical vapor deposition oxide stacked with an optimized thin anodic film, instead of a gate control structure, is used to control the planar surface potential of the implanted p+n diode under the weak inversion condition on the n-type surface and under weak accumulation on the p-type surface. The zero-bias resistance–area product is 7.6 × 104 Ω cm2 at 77 K. To the best of the authors' knowledge, this result represents the best performance of a small-area and implanted planar diode to date. The dark current is controlled by an internal shunt conduction mechanism, which seems to be related to the defects that are produced by the implantation. Low leakage current and high breakdown voltage have proven the feasibility of the composite anodic oxide/SiOx that is stacked as the passivation structure in small-pixel InSb p+n photodiodes for focal plane array applications. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Fermi level pinning-free interface at metals/homoepitaxial diamond (111) films after oxidation treatments

Schottky barrier heights of metal (Al, Au, Ni, and Pt) contacts on boron (B)-doped (111) homoepitaxial diamond films are investigated as a function of surface oxidation treatments before metal deposition [after wet-chemical oxidation (WO), WO followed by annealing in Ar atmosphere (WO-AN) and air oxidation]. It is found that the Schottky barrier height (ϕB) depends on the metal work function (ϕM) (Sϕ≡dϕB∕dϕM>0.3) on surfaces only after WO-AN, indicating that the interface at metals/B-doped (111) films after WO-AN has fewer defect states which do not pin the Fermi level. Experimental results and the appearance of a p-type surface conductive layer (SCL) are discussed and it is concluded that the pinning-free nature of the Fermi level is related to the appearance of a SCL.

Gas sensing properties of hydrogen-terminated diamond

Abstract Hydrogen-terminated diamond (HD) samples possess a p-type surface conductivity (SC) which is caused by transfer doping to an adsorbed liquid electrolyte layer. We report on gas sensing experiments on such samples and show that these selectively respond to analyte gases that can undergo electrolytic dissociation in the surface electrolyte layer. These gas sensing interactions occur at room temperature and are far more selective than sensing interactions at heated metal oxide layers. Successive substitution of surface hydrogen atoms by oxygen atoms causes the sensor baseline resistance and the gas-induced resistance changes to increase. This latter observation suggests that a small number of O-termination sites may have a catalytic effect on the gas sensing interactions. Increased temperature, O 3 and UV light exposure all reduce the sensor recovery time constants. Heating beyond the water evaporation threshold (∼200 °C) causes the surface electrolyte layer to disappear and the gas sensing effect to vanish. Re-adsorption of the surface electrolyte layer re-establishes both the sensor baseline resistance and the gas sensing effect. A model for the dissociative gas response is proposed that accounts for the observed experimental facts.

Hydrogen incorporation, bonding and stability in nanocrystalline diamond films

The hydrogen concentration in hot filament and microwave plasma CVD nanocrystalline diamond films is analysed by secondary ion mass spectrometry and compared to the film grain size. The surface and bulk film carbon bonds are analysed respectively by X-ray photoelectron spectroscopy (XPS) and ultra-violet Raman spectroscopy. XPS results show the presence of the hydrogenated p-type surface conductive layer. The respective intensities of the 1332 cm − 1 diamond peak, of the G and D bands related to sp 2 phases, and of the 3000 cm − 1 CH x stretching mode band, are compared on Raman spectra. The samples are submitted to thermal annealing under ultra-high vacuum in order to get hydrogen out-diffusion. XPS analysis shows the surface desorption of hydrogen. Thermal annealing modifies the sp 2 phase structure as hydrogen out diffuses.

P-type Surface Accumulation Layer of Hydrogen Terminated Diamond

The discovery process and the mechanism of p-type surface layer accumulation of hydrogen terminated diamond surfaces have been reviewed from the point of surface characterization and carrier formation near the subsurface. Since diamond is an insulating material, the surface density is as high as the order of 1013 cm−2 that is enough for high performance field effect transistors to be realized. The surface dipole formed by hydrogen-carbon bonds has a crucial role for the surface band structure of diamond. Also important is several types of negatively charged adsorbates necessary for charge neutrality condition and hole accumulation. New models for carrier emergence such as a transfer doping model have been discussed.

Excellent passivation of highly doped p-type Si surfaces by the negative-charge-dielectric Al2O3

From lifetime measurements, including a direct experimental comparison with thermal SiO2, a-Si:H, and as-deposited a-SiNx:H, it is demonstrated that Al2O3 provides an excellent level of surface passivation on highly B-doped c-Si with doping concentrations around 1019cm−3. The Al2O3 films, synthesized by plasma-assisted atomic layer deposition and with a high fixed negative charge density, limit the emitter saturation current density of B-diffused p+-emitters to ∼10 and ∼30fA∕cm2 on >100 and 54Ω∕sq sheet resistance p+-emitters, respectively. These results demonstrate that highly doped p-type Si surfaces can be passivated as effectively as highly doped n-type surfaces.

Effective passivation of highly aluminum-doped p-type silicon surfaces using amorphous silicon

Highly aluminum-doped p-type emitters prepared by screen printing on crystalline silicon wafers are effectively passivated by plasma-enhanced chemical-vapor deposited amorphous silicon layers. Using the photoconductance decay technique, the authors measure emitter saturation current densities of 800±200fA∕cm2 for nonpassivated emitters and of 490±120fA∕cm2 for Al-p+ emitters passivated with a 20nm thick amorphous silicon layer deposited at 225°C. An additional annealing step at 300°C for 10min reduces the emitter saturation current density down to only 246±60fA∕cm2. The measured saturation current densities are the lowest values achieved so far for Al-doped p+ emitter.

Gas Sensing Interactions at Hydrogenated Diamond Surfaces

Hydrogenated diamond (HD) samples exhibit a p-type surface conductivity (SC) which is caused by transfer doping to an adsorbed liquid electrolyte layer. We report on gas sensing experiments showing that such samples selectively respond to NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> gases at room temperature. Successive substitution of H-terminated surface sites by O-termination ones causes an increase in both the sensor baseline resistance and the gas-induced resistance changes. Thermal desorption of the surface electrolyte layer, on the other hand, causes the sensor baseline resistance to increase and the gas sensing effect to disappear. Readsorption of the surface electrolyte reestablishes both the sensor baseline resistance and the gas sensing effect. Our results indicate that the gas sensing effect is caused by local pH-changes due to acid/base reactions of the adsorbed gas molecules in the surface electrolyte layer. It is argued that this dissociative gas sensing mechanism represents a valuable complement with regard to the established surface combustion mechanism that is operative on heated metal oxide surfaces.

Investigation of acceptor states in ZnO by junction DLTS

Abstract We have realized a p-type ZnO surface layer by N + ion implantation of a high quality ZnO wafer and subsequent annealing. The conduction type of this surface layer was revealed by scanning capacitance microscopy. Rectifying current–voltage characteristics for processed devices were coherent with the existence of an internal pn junction. Deep donor- and acceptor-like defects were investigated by junction deep level transient spectroscopy. The donor-like levels correspond to those commonly observed for E1 and E3 defects. The acceptor states resolved have thermal activation energies of about 150 meV and 280 meV, respectively.

Investigation of 1/f Noise Mechanisms in Midwave Infrared HgCdTe Gated Photodiodes

In this work, gated midwave infrared (MWIR) Hg1–xCdx Te photodiodes are used to investigate the physical origin of 1/f noise generation. Gated photodiodes were fabricated on liquid-phase epitaxy p-type HgCdTe MWIR material with a vacancy-doped concentration of 1.6 × 1016 cm−3 and x = 0.31. CdTe was thermally deposited and used as both a passivant and a mask for the plasma-based type conversion, and ZnS was used as an insulator. Fabricated devices show a R0A of 1–5 × 104 Ωcm2 with zero gate bias. Application of 2 V to the gate improves the R0A by more than two orders of magnitude to 6.0 × 106 Ωcm2, which corresponds to the p-type surface being at transition between depletion and weak inversion. Trap-assisted tunneling (TAT) current was observed at negative gate biases and reverse junction biases. For gate biases greater than 3 V, a field-induced junction breakdown was observed. An In = αIβf −0.5 trend was observed above 200 pA reverse bias dark current, with α = 3.5 × 10−5 and β = 0.82, which corresponds to the TAT dominated region. Below 200 pA, junction generation-recombination (GR) current starts to dominate and this previously mentioned trend is no longer observed. Junction GR current was not seen to be correlated with 1/f noise in these photodiodes.

Fermi-level dependent morphology in photoinduced bond breaking on (1 1 0) surfaces of III–V semiconductors

The morphology of structural changes of InP(1 1 0)–(1 × 1) and GaAs(1 1 0)–(1 × 1) induced by electronic processes following laser excitation has been studied by scanning tunneling microscopy. Surface-vacancy clusters are predominantly formed on n-type surfaces, while isolated anion monovacancies are generated almost exclusively on p-type surfaces. This remarkable Fermi-level effect in the morphology is characterized in terms of a screened Coulomb type interaction between charged surface monovacancies and carriers generated by laser excitation. It is shown that localization of photogenerated valence holes induces electronic bond rupture at surface sites.

Surface electronic properties on boron doped (111) CVD homoepitaxial diamond films after oxidation treatments

Surface electronic properties on oxidized boron (B) doped (111) homoepitaxial diamond films are investigated by Hall effect measurements and Schottky junction characterizations. Surface electronic properties on (111) diamond strongly depend on annealing treatments after wet-chemical oxidation, whereas for those on (001) diamond no change due to annealing can be detected. Hall effect results show that a p-type surface conductive layer (SCL) exists on (111) diamond surface in air after wet-chemical oxidation followed by annealing in Ar atmosphere (WO–AN) above 300 °C, but does not if only wet-chemical oxidation or air-oxidation is applied. This SCL disappears at annealing temperature above 350 °C in air. Schottky junction characteristics suggest that the Fermi level is unpinned at the (111) surface after WO–AN. Surface electronic characteristics on (111) diamond after WO–AN are similar to those generated by hydrogen termination.

Performance Improvement and Mechanism of Chlorine-Treated InGaN–GaN Light-Emitting Diodes

The electrical and optical performances of multiple-quantum-well (MQW) light-emitting diodes (LEDs) were improved by using chlorine to treat the surface of the p-type layer. The chlorine was produced from electrolyzing diluted . The chlorine reacted with the p-type surface and induced Ga vacancies in the surface region. The specific contact resistance of was obtained for metals contact with the chlorine-treated p-type due to the creation of more hole carriers via the inducement of Ga vacancies. Compared with the untreated LEDs, the current-voltage characteristics showed that the forward voltage of the chlorine-treated MQW LEDs decreased from 3.3 to at a driving current of , and the light output power increases 1.25 times at . The reverse leakage current of the chlorine-treated MQW LEDs was also significantly decreased due to the passivation of surface states by chlorination treatment of p-type layer.

A High Schottky-Barrier of 1.1 eV Between Al and S-Passivated p-Type Si(100) Surface

We report a high Schottky-barrier between Al and S-passivated p-type Si(100) surface. Capacitance-voltage measurements indicate a barrier height of 1.1 eV, while activation-energy measurements suggest 0.94-0.97 eV. Possible reasons for the discrepancy are proposed. The barrier height of 1.1 eV suggests degenerate inversion on the p-type Si surface, and Fermi statistics is used to describe its electrostatics. Although fabricated like a Schottky diode, this Al/S-passivated p-type Si(100) device works like a p-n junction diode. Temperature-dependent current-voltage measurements reveal that S passivation reduces the reverse saturation current of Al/p-type Si(100) diodes by over six orders of magnitude