Passivation Of Acceptors Research Articles

Passivation of dopants in InGaP using ECR hydrogenation

Hydrogen passivation of Zn acceptors and Si donors in In 0.49Ga 0.51P layers has been examined as a function of the microwave power (0–1000 W) and process pressure (1–10 mTorr) of electron cyclotron resonance H 2 discharges. The dopant passivation is much stronger in p-type InGaP than in n-type materials for all plasma conditions, which we ascribe to the more stable bond-centred position for hydrogen in p-InGaP. Reactivation of the passivated dopants begins at ⩽ 300 °C and is complete by 400 °C in n-type material and 450 °C in p-type material.

Effect of hydrogen passivation on Be-doped AlGaAs/GaAs quantum wells

Hydrogen passivation of high quality AlGaAs/GaAs:Be quantum wells (QWs) is studied by photoluminescence (PL) spectroscopy. The interaction of hydrogen with both Be dopants and QW interfaces is analyzed. The efficiency of Be acceptor passivation by hydrogen is shown to be dependent on the Be concentration. By comparing the PL spectra of the QW structures with different doping level, before and after hydrogenation, a partial (up to 50%) deactivation of Be atoms is revealed. It is also shown that a prolonged hydrogenation strongly degrades the interface sharpness, presumably due to hydrogen-enhanced intermixing.

Surface Fermi level position of hydrogen passivated Si(111) surfaces

Core and valence band photoemission data of hydrogen passivated Si(111):H surfaces yield surface Fermi level positions that are indicative of a near-surface depletion layer for n- as well as p-type samples. The bulk Fermi level positions are attained after annealing at ∼400 °C. These observations are explained in terms of a hydrogen induced passivation of donors and acceptors in a surface layer of the order of a μm as a result of the wet-chemical etching procedure.

Effects of annealing atmosphere and temperature on acceptor activation in ZnSe:N grown by photoassisted MOVPE

Effects of annealing atmosphere and temperature on acceptor activation in nitrogen-doped ZnSe layers grown by photoassisted metalorganic vapor-phase epitaxy (MOVPE) have been investigated. It is shown that as-grown high resistive layers are converted to p-type by thermal annealing in N2 atmosphere in the temperature range from 500 to 550°C, while they do not if annealed in atmospheres of H2, diethylzinc (DEZn), and dimethylselenide (DMSe) in which hydrogen is contained. The net acceptor concentration NA − ND has reached up to 4 × 1017cm−3 by the thermal annealing at 500°C, but it is lower when annealed at 550°C. By exposing to H2 atmosphere at 350°C, NA − ND decreases with the exposure time. However, it almost recovers to the value obtained by the first annealing in N2, if the layer is annealed again in N2 atmosphere at 500°C. These results are discussed based on the hydrogen passivation model, i.e. the dehydrogenation and hydrogenation occur reversibly and result in activation and passivation of nitrogen acceptors, respectively.

Direct observation of nitrogen acceptor passivation in ZnSe by hydrogen plasma

Passivation effects of nitrogen acceptor in hydrogenated ZnSe are investigated with low-temperature photoluminescence. Nitrogen-doped samples were exposed to a hydrogen plasma produced by an rf plasma cell. The significant PL spectral change indicates that hydrogen neutralizes the activity of nitrogen acceptors in ZnSe. This is the first observation of intentional hydrogen passivation of nitrogen acceptors in ZnSe, which plays an important role in determining the p-type conductivity of ZnSe grown by metalogranic chemical vapor deposition.

Comparison of hydrogen passivation of ZnSe:N using gas source and conventional molecular beam epitaxy

The use of various gaseous source epitaxial techniques for the growth of II–VI compounds, such as metalorganic vapor phase epitaxy (MOVPE) or gas source molecular beam epitaxy (GSMBE), offers the promise of improved flux control and source flexibility. However, passivation of the nitrogen acceptors by hydrogen (which is usually present in abundance in these growth environments) has proven to be a major obstacle in the successful application of MOVPE and GSMBE for the growth of highly conductive p-type ZnSe. Although there have been a few reports of successful nitrogen doping of ZnSe:N by GSMBE and MOVPE, the mechanisms of hydrogen incorporation, and its dependence on the growth conditions as well as post-growth treatments, are still unclear. In this paper, we will compare the hydrogen passivation behavior in ZnSe:N grown by: (1) GSMBE using H2Se and elemental Zn as sources; and (2) conventional molecular beam epitaxy (MBE) with intentional introduction of hydrogen. A comparison of the electrical properties existing between the GSMBE-grown ZnSe:N films with those grown by MBE with an intentional flux of hydrogen will be presented.

プロセス雰囲気と表面制御 ＶＩ族水素化物とＩＩ族金属とを原料としたＩＩ‐ＶＩ族化合物のガスソース分子線エピタキシー

II-VI blue-green laser diodes have attracted much attention for use as lightsources for future optical disc systems. Epitaxial growth of ZnSe-based mterials using a gaseous source is required, because the elements comprising these materials have high vapour pressures. To date, attempts at growth of p-type low-resistivity layers using a gas source have been unsuccessful due to passivation of acceptors by hydrogen in the sources. We describe conditions for growth of p-type ZnSe-based materials by gas source molecular beam epitaxy with a solid source of group II elements, a hydride gas of a group VI element and nitrogen activated by rf plasma. The acceptor concentrations of the grown layers are comparable to those grown by solid source molecular beam epitaxy. Using the low-resistivity p-type layers, pulse oscillation of a ZnCdSe/ZnMgSSe laser diode is attained at 200 K.

Effect of growth temperature on the electrical properties of CCl4-doped semi-insulating InP

The electrical properties of semi-insulating InP epitaxial layers grown by metalorganic chemical vapor deposition using CCl4 as a doping source have been studied as a function of the growth conditions of the material. Secondary ion mass spectrometry has been used to analyze the incorporation of impurity species in these layers. These measurements indicate that the resistivities of the CCl4-doped InP layers increase exponentially (exceeding 1012 Ω cm) with increasing growth temperature. The incorporation of C, H, and Cl decreases in these layers. In conjunction with the dependence of the resistivity on the flow rate of the diluted CCl4 dopant during growth, these results suggest that the semi-insulating nature of the InP layers is due to CCl4-mediated incorporation of one or more defects during growth. It is not likely that either a deep level created by Cl or hydrogen passivation of shallow donors and acceptors is responsible for the electrical properties of this material.

Hydrogen passivation of Mg acceptors in GaN grown by metalorganic chemical vapor deposition

The effects of the deliberate hydrogenation of GaN were investigated for heteroepitaxial layers grown by metalorganic chemical vapor deposition. The GaN layers were either Mg-doped, p-type after thermal activation, or Si-doped, n type. Elemental depth profiles from secondary ion mass spectroscopy reveal a striking contrast after a deuteration at 600 °C: the deuterium concentration in Mg-doped GaN is ∼1019 cm−3 while there is no detectable deuterium incorporation in the n-type material. Variable temperature Hall effect measurements provide the most direct evidence to date for Mg–H complex formation with the decrease in the hole concentration upon hydrogenation accompanied by an increase in the hole Hall mobility.

Hydrogen passivation of donors and acceptors in SiC

The effect of hydrogen on donors (N) and acceptors (Al, B) in 6H-SiC crystals has been evidenced by electron spin resonance and transport measurements. Typical passivation (i.e., complexing with H) levels of 75% have been obtained by annealing in a H2 atmosphere, and a corresponding decrease in free-carrier density has been observed.

Enhanced hydrogenation and acceptor passivation in Si by pressurized water boiling

It has been shown that a pressurized water boiling (PWB) at 2 atmospheric pressures and 120 °C in an autoclave vessel accelerates significantly hydrogenation and neutralization of B acceptors in Si. Compared with boiling at atmospheric pressure, PWB reduces more the free-hole IR absorption and increases more the sheet resistivity in B implanted p+ layer on n-type substrate. An IR absorption of B–H stretching vibration (∼1907 cm−1) has been detected at 16 K for a p+ layer which was PWB processed for only 6 h. Concentration increase of H-related species in water and faster diffusion of H in Si at higher temperature may be the cause. In contrast with other hydrogenation techniques, water boiling hardly passivates donors in Si even for 10 h PWB.

Effect of hydrogenation and thermal annealing on the photoluminescence of p-InP

The effect of hydrogenation and thermal annealing on the photoluminescence (PL) of InP:Mg and InP:Zn is presented. On hydrogenation, a rise in near-band-edge PL intensity by a factor of 16 for the InP:Mg sample and a factor of 50 for the InP:Zn sample is observed and this is attributed to the passivation of nonradiative centers. A donor–acceptor pair transition before hydrogenation in the InP:Mg sample and after hydrogenation in the InP:Zn sample was observed. In both cases, the magnitude of the shift in peak position with excitation intensity shows the involvement of a donor deeper than the normally present shallow donors. The ionization energy of the donor in InP:Mg is estimated to be 48 meV and that in InP:Zn is estimated to be <40 meV. No hydrogenation induced radiative transitions were observed. In the InP:Mg samples, the acceptor passivation effects are lost after annealing at a temperature of 350 °C for 2 min, whereas the nonradiative center passivation after hydrogenation is not completely lost. In InP:Zn, the acceptor passivation along with nonradiative and deep center passivation are lost after an annealing treatment of 300 °C for 2 min. A thermally induced D–A pair emission in InP:Zn which moves to lower energies with increasing annealing temperature is observed. Such a transition is not observed for InP:Mg. This can be either due to a preferential pairing of the donor and acceptor which becomes randomized after the heat treatment or due to the removal of hydrogenation effects by annealing.

Hydrogen passivation caused by “soft” sputter etch cleaning of Si

Soft sputter etch cleaning of p-type silicon (self bias range 50–150 V) causes hydrogen passivation of boron acceptors over a depth range in the order of 1 μm. Annealing at 200°C reactivates the boron dopants. Assuming hydrogen diffusion in the RTA temperature range 155–175°C we derive a hydrogen diffusion coefficient which is in good agreement with values known from literature. The diffusion activation energy obtained is 0.65 ev. Mobility measurements show an increase of mobility after sputter etching, proving that passivation and not compensation is causing the effective B-concentration reduction.

Lithium passivation and electric-field-assisted reactivation of acceptors in GaAs.

We performed reverse-bias annealing of Schottky diodes on GaAs samples in which Zn and Cu acceptors had been partially passivated by Li diffusion. Using capacitance-voltage and deep level transient spectroscopy measurements we observed thermal dissociation of Zn-Li and Cu-Li complexes in the electric field of reverse-biased junctions and a consequent increase of electrically active acceptors in the depletion region of the diodes as well as enhanced passivation of acceptors in the low-field region of the depletion layer and in the neutral bulk. The direction of the electric field is consistent with lithium drifting as a positively charged ion in p-type GaAs. We also investigated the interaction between lithium and the reactivated acceptors under zero-bias conditions. The effect of zero-bias annealing between room temperature and 150 \ifmmode^\circ\else\textdegree\fi{}C on both the shallow Zn and the deep Cu acceptors was found to be consistent with a mobile ionized ${\mathrm{Li}}_{\mathit{i}}$ donor passivating negatively charged acceptors through Coulomb interaction.

Lithium–gold-related defect complexes in n-type crystalline silicon

Using deep level transient spectroscopy combined with secondary-ion-mass spectroscopy and capacitance–voltage profiling, it is demonstrated that lithium diffusion into gold-doped n-type silicon at temperatures between 200 and 300 °C results in the formation of two lithium–gold-related complexes. One of the Au–Li complexes appears to be electrically passive and is observed indirectly as gold acceptor passivation. Virtually all passivated gold acceptors are reactivated after 30 min annealing at 400 °C of samples with comparable Au and Li concentrations in the 1014 atoms/cm3 range. The process can be reversed again by additional heat treatment at lower temperatures. The passivation–reactivation cycle can be repeated as long as there is enough Li present in the crystal. This reaction can be described by a mass-action law between negatively charged gold atoms and positively charged lithium (Au−+Li+) with a free binding energy of approximately 0.87 eV. The other Au–Li complex has a deep level (labeled L1) within the silicon band gap with an activation energy of 0.41 eV. The L1 signal is strongest after annealing at temperatures between 250 and 300 °C but weaker at lower temperatures where the electrically passive Au–Li complex is favored. From the dissociation kinetics of L1 during reverse bias annealing it is deduced that the complex consists of one gold atom and one or more lithium atoms. Finally, using DLTS depth profiling it is observed that injection of hydrogen into the sample surface region by wet chemical etching results in deactivation of the L1 trap.

Hydrogen passivation of cd acceptors in III–V semiconductors studied by PAC spectroscopy

Formation, structure, and stability of hydrogen correlated complexes, created at Cd acceptors in GaP, InP, and InAs have been studied after plasma charging as well as after H + and/or He + implantation at different energies. The different complexes were monitored by the perturbed angular correlation technique (PAC). In InP and Gap, the stability of Cd-H pairs is very similar for comparable Cd concentrations (E D = 1.4(2) eV and E D = 1.5(1) eV). In InAs, two different hydrogen correlated configurations are observed, one could be identified as Cd-H pair, oriented in 〈111〉 lattice direction ( ν Q = 427 MHz, η = 0). The second complex involves at least one H atom and radiation defects or, favoured by a defect induced, secondary mechanism several hydrogen atoms.

Optical and electrical properties of hydrogen-passivated gallium antimonide.

The effect of hydrogen-plasma passivation on the optical and electrical properties of gallium antimonide bulk single crystals is presented. Fundamental changes of the radiative recombination after hydrogenation in undoped, zinc-doped, tellurium-doped, and codoped (with Zn and Te) GaSb are reported. The results of optical measurements indicate that passivation of acceptors is more efficient than that of the donors and, in general, the passivation efficiency depends on the doping level. Passivation of deep nonradiative centers is reflected by the gain of photoluminescence intensity and decrease in deep-level transient spectroscopy peak height. Extended defects like grain boundaries and dislocations have also been found to be passivated. The thermal stability of the passivated deep level and extended defects is higher than that of the shallow level. The kinetics of thermally released hydrogen in the bulk has been studied by reverse-bias annealing experiments.

Effect of Hydrogenation on the Electrical and Optical Properties of GaSb

AbstractThe effect of hydrogen plasma treatment on the optical and electrical properties of Gallium Antimonide bulk single crystals is presented. Plasma exposure gives rise to a layer of defects on the surface. These defects introduce multiple trap levels in the band gap from which a slow emission of carriers is observed during the capacitance - voltage measurements. On removal of the defect layer by controlled etching, the effects of hydrogen passivation are seen. The results of optical measurements indicate that passivation of shallow acceptors is more efficient than that of the donors and in general the passivation efficiency depends on the doping level. Passivation of deep levels and extended defects like grain boundaries and dislocations has also been observed. The thermal stability of the passivated deep level and extended defects is higher than that of the shallow level.

Annealing effects on hydrogen passivation of Zn acceptors in AlGaInP with p-GaAs cap layer grown by metalorganic vapor phase epitaxy

We have investigated the hydrogen passivation mechanism of Zn acceptors in a p-AlGaInP layer with a p-GaAs cap layer, grown by metalorganic vapor phase epitaxy (MOVPE), by observing post-epitaxial annealing effects on the activation of Zn acceptors. The post-epitaxial annealing was carried out in ambiences containing hydrogen, arsine, and phosphine gas in the temperature range of 300–750°C. The activation of Zn acceptors depended strongly on the cooling conditions after the annealing and the p-GaAs cap layer thickness. These phenomena are associated with the atomic hydrogen which is released from the arsine by decomposition and diffuses into the p-AlGaInP layer to form the P-H bonds through the p-GaAs cap layer in the temperature range of 400–500°C during cooling step after the post-epitaxial annealing.

Mechanism of Zn passivation in AlGaInP layer grown by metalorganic chemical vapor deposition

The mechanism of passivation effect on the hole concentration in Zn-doped (Al 0.7Ga 0.3) 0.5In 0.5P layers grown by metalorganic chemical vapor deposition (MOCVD) is investigated. It is found that oxygen concentration in AlGaInP should be suppressed under 5 x 10 16 cm -3 in order to make the passivation behavior clear without effect of oxygen contamination, which was controlled by employing a high-grade gas purifier. The passivation of zinc acceptors has been effectively avoided by optimizing of the cooling atmosphere. The hole concentration increased with raising the AsH 3 flow stopping temperature after growth and it saturated at above 500°C. High hole concentration (beyond 1 x 10 18 cm -3) was achieved by combining the anti-passivation technique and the oxygen control techniques. We suggest from the hole concentration dependence on the measuring temperature that the new deep acceptor level due to the Zn passivation causes the hole concentration reduction in the AlGaInP layer.