Showing papers by "Stephen J. Pearton published in 1987"

Vibrational characteristics of acceptor‐hydrogen complexes in silicon

Abstract: Acceptor‐hydrogen complexes for the group III acceptors, B, Al, and Ga, in Si have been studied with low‐temperature infrared spectroscopy. The Si‐H stretching band narrows dramatically upon cooling to low temperature thereby aiding the detection of the vibrations of the Al and Ga acceptor‐H complexes. The frequency 2201 cm−1 we have measured for the Al‐H complex is in reasonable agreement with the prediction made by G. G. DeLeo and W. B. Fowler [Phys. Rev. B 31, 6861 (1985)] (2220 cm−1 for a 〈111〉 interstitial configuration for the H). Assignment of the new vibrational bands is confirmed by isotopic substitution. The strength of the absorption provides evidence that the passivation is not the result of compensation alone and that a major fraction of the passivated acceptors result in acceptor‐H complexes. A new, low‐energy excitation of the acceptor‐hydrogen complexes gives rise to a sideband to the main stretching vibration and explains the pronounced energy shift and narrowing of the spectra upon cooli...

Passivation of Si donors and DX centers in AlGaAs by hydrogen plasma exposure

Abstract: The effect of hydrogen plasma exposure upon shallow donors and DX centers in silicon‐doped AlGaAs has been investigated by deep level transient spectroscopy and capacitance versus voltage measurements. Following exposure to a hydrogen plasma for 30 min at 250 °C, the shallow level and DX center activity are reduced by an order of magnitude throughout a 1.6‐μm‐thick layer of molecular beam epitaxially grown AlGaAs. Isochronal annealing studies showed that both the shallow donor and DX center electrical activity recover together at about 400 °C. The shallow donor recovery mimics the behavior of donors in GaAs and has an activation energy of 2.0 eV. The DX center recovery shows a distribution of activation energies centered at 2.1 eV with a full width at half‐maximum of 0.25 eV. The hydrogen passivation chemistry of DX centers and shallow donors support models in which isolated Si impurities give rise to both DX behavior and shallow levels.

Ion implantation in GaAs

Abstract: Recent advances in the understanding of the relationship between implanted dopant solubility and electrical activity in GaAs are reviewed and direct lattice configuration measurements explaining these results are presented. The nature of residual defects remaining after activation annealing of GaAs, in particular rapid thermal annealing, are discussed, along with a review of the application of ion beams in promoting compositional disordering of GaAs-AlAs superlattices. The outstanding problems remaining in the use of ion implantation technology for GaAs are also detailed.

Hydrogenation of GaAs on Si: Effects on diode reverse leakage current

Abstract: Plasma hydrogenation for 3 h at 250 °C of GaAs layers grown directly on Si substrates by metalorganic chemical vapor deposition, followed by a 5‐min, 400 °C anneal to restore the passivated shallow donor electrical activity, increases the reverse breakdown voltage of Schottky diode structures from 2.5 to 6.5 V. This improvement appears to be a result of the passivation by atomic hydrogen of defects such as threading dislocations caused by the large (4%) lattice mismatch between GaAs and Si. A reduced Schottky barrier height is exhibited by hydrogenated samples, consistent with As depletion of the surface occurring during the long duration plasma processing.

Electrical activity of defects in molecular beam epitaxially grown GaAs on Si and its reduction by rapid thermal annealing

Abstract: The electrical activity of defects in GaAs grown on Si by molecular beam epitaxy (MBE) has been examined by studying the diode characteristics and deep level transient spectroscopy (DLTS) of Schottky barriers. The defects are not apparent from the forward bias diode characteristics but they are indicated by large leakage current and early breakdown under reverse‐biased conditions. Post‐growth rapid thermal annealing (RTA) has been found to significantly improve the diode behavior making it almost comparable to GaAs‐on‐GaAs. The reverse current in the as‐grown material shows a very weak temperature dependence, indicating that its origin is not thermionic emission or carrier generation. It is speculated that a large part of this current is due to defect‐assisted tunneling, which is reduced by RTA. DLTS indicated only a modest increase in the concentrations of the well‐known electron traps typical of MBE GaAs with no evidence for new levels in the upper half of the band gap.

Hydrogen Injection Into P-Type Silicon By Chemical Etching

Abstract: Hydrogen injection with B acceptor neutralization in p-type Si etched in HNOs and HF acid mixtures has been confirmed by isotopic [D] substitution and secondary ion mass spectrometry [SIMS] profiling. Quantitative measurements of the near-surface Injected hydrogen were made following field-aided, in-bulk transport [H + drift] in reverse-bias annealed Schottky diodes from etched, B-doped Si. Chemical-etch injection is found to be self limiting with neutralization observed over a depth which is characteristic of the base material acceptor concentration and in the range 6–8 extrinsic Debye lengths, indicating that holes are essential in the injection mechanism. An effective diffusivity for hydrogen in etched p-Si of ∼ 2 × 10 −9 cm 2 s −1 was measured [300 K], considerably higher than previously reported.

Characterization of GaAs layers grown directly on Si substrates by metalorganic chemical vapor deposition

Abstract: The electrical and structural properties of GaAs layers grown directly by metalorganic chemical vapor deposition on Si substrates oriented 2° off (100) toward [011] are reported. The uniformity of minority‐carrier lifetime in the 2 in.‐ diam heteroepitaxial wafers is comparable to that in bulk GaAs of the same doping density (2×1016 cm−3). Selective etching of the GaAs layer reveals an etch pit density of ∼108 cm−2, consistent with plan view transmission electron microscopy which shows a defect density of ∼108 cm−2. Rapid annealing at 900 °C for 10 s does not significantly alter the heterointerface abruptness, and at the same time the crystalline quality of the GaAs improves slightly. The deep level concentration in the as‐grown layer is ∼1013 cm−3 as determined by capacitance spectroscopy. Finally, the activation characteristics of low dose Si implants (3×1012 cm−2 at 60 keV) are similar to those in high quality bulk GaAs.

Heterointerface stability in GaAs‐on‐Si grown by metalorganic chemical vapor deposition

Abstract: The stability of the electrical and structural properties of GaAs directly deposited on Si by metalorganic chemical vapor deposition is examined. Extended annealing at 900 °C leads to substantial diffusion of Si across the heterointerface while under the same conditions there is no significant motion of Si incorporated as a dopant into the GaAs surface region. The degree of enhancement of Si diffusion ranges from a factor of ∼250 for 0.5‐μm‐thick GaAs films to ∼5 for 4‐μm‐thick films. The annealing time and GaAs layer thickness dependence of Si diffusivity near the interface is consistent with a defect‐modulated mechanism. A large fraction of this mobile Si is electrically inactive.

Interaction of hydrogen and thermal donor defects in silicon

Abstract: We have studied the interaction of hydrogen with thermal donors in silicon using transient capacitance and current spectroscopy. We find that a large degree of thermal donor passivation (a factor of 40) can be achieved by hydrogen plasma exposure at 120 °C. The residual electrical activity is shown to arise from perturbed E(0.07) and E(0.15) donor states. Annealing at 200 °C almost completely reactivates the low concentration of thermal donors present in these samples. A model involving different incorporation sites for hydrogen is proposed to explain the results.

Local structure of S impurities in implanted GaAs

Abstract: The local structure of S implanted at high doses (10 15 −10 16 cm −2 , 100 keV) into GaAs and annealed at 900°C has been determined by extended X-Ray absorption fine structure by monitoring the S (K α ) fluorescence yield. The S first neighbor shell shows a significant static broadening compared to the S second and third shells. This indicates two S configurations of approximately equal population: (1) substitutional S on an As site and (2) a complex formed by S on an As site and an As vacancy on the second shell with a S-first neighbor distance relaxation of 0.14 ± 0.04 A. The two-site configuration explains the well-known disparity between implanted S concentration and net electrical activity, a phenomenon which occurs at high concentrations for all donor species implanted in GaAs.

Ion-implantation and activation behavior of Si in MBE-Grown GaAs on Si substrates for GaAs MESFET's

Abstract: The suitability of MBE-grown GaAs layers on Si substrates has been studied for ion-implanted GaAs MESFET technology. The undoped as-grown GaAs layers had a carrier concentration below 1014cm-3. Uniform Si ion implants into 4-µm-thick GaAs layers on Si were annealed at 900°C for 10 s, using a rapid-thermal-annealing (RTA) system. Both the activation and the doping profile were similar to those obtained in bulk semi-insulating GaAs under similar conditions. The SIMS profiles of Si and As atoms near the GaAs/Si heterointerface were identical before and after the RTA process, indicating negigible interdiffusion during the implant activation. Dual implants of a shallow n+ layer and an n-channel layer were used to fabricate GaAs MESFET's with a recess-gate technology. Selective oxygen ion implantation was used for device isolation. The maximum transconductance obtained was 135 mS/ mm compared to typical values of 150-180 mS/mm obtained in our laboratory on GaAs substrates in similar device structures.

Activation characteristics and defect structure in Si‐implanted GaAs‐on‐Si

Abstract: Undoped metalorganic chemical vapor deposited GaAs layers on Si substrates were implanted with 29Si ions (5×1012 cm−2 dose at 100 keV energy) to form a shallow n‐type region. The net donor activation (74%) and electron mobility (3014 cm2 V−1 s−1) after rapid thermal annealing (900 °C, 10 s) were compared to those obtained for similar implants into bulk GaAs. There was a slight improvement in the proton backscattering yield from the GaAs‐Si interface region after the annealing cycle, consistent with cross‐sectional transmission electron microscopy data showing an alignment of defects in annealed samples.

Hydrogen in Silicon

Abstract: We summarize the recent results in hydrogen passivation in silicon, including presenting comprehensive diffusion profiles, i.e., profiles in floating zone n-type and p-type silicon vs resistivity. Domination of hydrogen diffusion by impurity trapping is clearly indicated for part of the profile in low resistivity p-type Si. Also mentioned are the current models of hydrogen passivation of dangling bonds, shallow acceptors, shallow donors, and hyper-deep defects.

Characterization of GaAs grown by metalorganic chemical vapor deposition on Si‐on‐insulator

Abstract: Epitaxial GaAs layers were grown by metalorganic chemical vapor deposition on Si‐on‐insulator structures formed by high dose oxygen implantation The quality of the GaAs films was examined as a function of layer thickness (001–4 μm) The surface morphology, ion backscattering yield, x‐ray diffraction peak width, and Si implant activation efficiency all improve substantially with GaAs thickness At a film thickness of 4 μm many of these properties are comparable to bulk GaAs, but some cracking of the epitaxial film is evident Cross‐sectional transmission electron microscopy reveals an average defect density of ∼108 cm−2 in the GaAs layer, which is similar to the density in GaAs films grown directly on Si

Passivation of N-Type Silicon by Hydrogen

Abstract: Infrared spectroscopy has been used to study hydrogen passivation of P, As, and Sb donors in Si. The spectra show several new absorption bands due to donor-H complexes. By comparing spectra after different heat treatments it is shown directly that the passivation is due to complex formation.

Annealing behavior of Ga+ implanted GaAs/AlGaAs observed by transmission electron microscopy

Abstract: The structural aspects and annealing behavior of induced damage by Ga+ ion implantation of a GaAs single quantum well as investigated by transmission electron microscopy are presented. After rapid thermal annealing, vacancy and interstitial perfect dislocation loops are found on 〈110〉 and 〈111〉 type planes. In contrast to previous results from superlattices of AlGaAs/GaAs, we find dislocation loops in the AlGaAs as well as in the GaAs layer. The cathodoluminescence intensity of the implanted quantum well recovers completely after annealing.

Redistribution of Implanted Hydrogen in p+ GaAs(Zn) and n+ GaAs(Si) Crystais

Abstract: In order to gain a better understanding of hydrogen in GaAs crystals, a Zn doped p+ GaAs wafer has been implanted with 300 keV protons (H) to a fluence of 1E16/ain and portions of the wafer have been furnace annealed at temperatures up to 600 °C. The implanted H and the dopant Zn atomr were then depth profiled using secondary ion mass spectrometry (SIMS). The measurements show that the H redistributes itself in the p+ GaAs(Zn) in much the same manner as it does in n+ GaAs(Si). Movement of the implanted H begins with annealing at 200°C and proceeds rapidly with higher temperatures. However, based on the SIMS profiles, the diffusion coefficient for the H diffusing into the undamaged p+ GaAs(Zn) crystal appears to be considerably higher than that of H into n+ GaAs(Si). Electronic properties of the inplanted and annealed p+ GaAs samples have also been examined and correlated with the SINE profiles.

MO-CVD GaAs Grown by Direct Deposition on Si

Abstract: GaAs layers were grown directly on misoriented (2° off (100)→[011]) Si substrates by Metalorganic Chemical Vapor Deposition. The threading dislocation density at the surface of 4 μm thick layers was typically 108cm−2, as determined by both preferential etching and transmission electron microscopy. Rapid thermal annealing (900°C, 10s) improved the crystalline quality of the GaAs near the heterointerface while allowing no detectable Si diffusion into this layer. Two deep electron traps were observed in the undoped GaAs, but were present at a low concentration (∼ 1013 cm−3 ). The (400) x-ray diffraction peak width from the GaAs was significantly reduced with increasing GaAs layer thickness, indicating improved material quality. This is supported by Si implant activation data, which shows higher net donor activity in thicker layers.

Implanted Dopant-Defect Interactons in GaAs

Abstract: The implantation temperature dependence of dopant solubility and electrical activity was investigated for Sn, Cd and Te ions in GaAs. Implantation doses of 5×10 12 – 5×10 15 cm −2 were performed in the temperature range from LN 2 to 400°C, followed by rapid thermal annealing (950°C) or furnace annealing between 650°C and 850°C. Solubilities above 10 20 cm −3 were obtained for all of the species, with a peak value of 2.5×10 21 cm −3 for Te after 850°C furnace annealing. However essentially no correlation existed between dopant solubility and electrical activity or between electrical activity and the high density of defects remaining after many of the annealing cycles. This emphases the role of fine scale, point defect complexes in controlling the electrical activity of implanted dopants in GaAs.

Formation of p+ and High Resistivity Regions in GaAs-AIGaAs Heterojunctions

Abstract: The formation of p+ and high resistivity layers in GaAs-AIGaAs heterostructures is useful in a number of applications, including the fabrication of heterojunction bipolar transistors (HBTs). Control of the implanted dopant profile during annealing is paramount for rapidly diffusing acceptor species such as Be and Mg, and we show SIMS data of the dopant profile in implanted heterojunctions as a function of annealing temperature in the range 700–900°C for 1–5 sec. Annealing of implanted Be at ≥800°C even at a dose of 2×10l5cm−2 results in complete activation whereas Mg shows only 30% activation under these conditions. There is no significant interface disordering visible by TEM or RBS for either case. Multiple energy O implants (up to and including 1 MeV) were used to render the entire heterostructure resistive; for doses of ∼1013cm−2, the O bombarded layers showed resistivities of 108 Ω/□ after 525°C annealing.

Semiconductor Superlattices: Order and Disorder

Abstract: We review and discuss the main structural phenomena inherent in epitaxial multilayer semiconductor growth: lattice mismatch, misfit dislocation generation, two-dimensional vs. threedimensional growth, interface abruptness and planarity and the local atomic structure of semiconductor alloys. The prevalence of metastable structures, often a function of crystal growth temperature, is discussed. We also investigate the effect of Si ion implantation and subsequent rapid thermal annealing of AlGaAs/GaAs and InGaAs/GaAs multilayer structures, with reference to strain relaxation, layer planarity and enhanced Al, In and Si diffusion.

Extended X-ray Absorption Fine Structure Studies by Soft X-ray Fluorescence Detection

Abstract: Comparison of x-ray fluorescence and electron-yield surface extended x-ray absorption fine struction (EXAFS) above the S K-edge for c(2 × 2)S on Ni(100) reveals an order of magnitude higher sensitivity for the former technique due to a much lower background. The higher sensitivity of soft x-ray fluorescence EXAFS opens the possibility of structural studies on very dilute atomic species on surfaces (< 0.1 monolayer) or in the bulk (< 1019 atoms/cm3) of a different material. An EXAFS study on the local structure of S impurities in GaAs is presented as an example of such studies. We derive the local geometry around the S atoms finding two competing configurations of approximately equal population: (1) substitutional S on an As site (2) a complex formed by S on an As site and an As vacancy on the second shell with a S-first neighbor distance relaxation of 0.14 ± 0.04 A. The two configurations explain the disparity between implanted S concentration and net electrical activity.

Semiconductor structures including quantum well wires and boxes

Abstract: A method of fabricating semiconductor structures, quantum well wires and boxes is described in which interdiffusion in a semiconductor having a compositional profile is enhanced by the presence of defects created by ion implantation in localized regions. A representative structure is shown in Fig. 5.

Lattice-Matched Gaas/Ca0.45Sr0.55F2/Ge(100) Heterostrucuures Grown By Molecular Beam Epitaxy

Abstract: Epitaxial, lattice-matched GaAs/Ca 0.45 Sr 0.55 /F 2 heterostructures were grown on Ge(100) substrates by molecular beam epitaxy. The films were analyzed by Rutherford backscattering and secondary ion mass spectroscopy to determine crystallinity and Ge outdiffusion. The X min (channeling over random yield) of a 1.5 μm-thick GaAs film grown on the fluoride is 0.075, indicating reasonably good epitaxy. After rapid thermal annealing, the crystallinity of higher-X min films improves, and Ge diffuses only 200 A into the fluoride, indicating that a thin fluoride layer is an effective barrier to Ge outdiffusion.

Extended X-Ray Absorption Fine Structure Studies of Impurities in Semiconductors

Abstract: We discuss Extended X-ray Absorption Fine Structure (EXAFS) experiments on impurities in semiconductors. The local structure of the impurity site is determined for the first, second and third neighbor shells. These studies are carried out on absorption edges in the soft x-ray region using a novel fluorescence detection scheme which reveals improved detection sensitivity when compared with more standard electron Auger yield methods. The higher detection sensitivity allows structural studies at atomic densities as low as 1018 at/cm3 and this technique is used to study the local structure of P and S impurities in GaAs and of S in AlxGa1-xAs at concentrations of 1019–1020 at/cm3. The P atoms are substitutional on As sites, and a breathing relaxation of the P first shell Ga atoms is responsible for a P-Ga distance of 2.38A, which is 0.07A shorter than the As-Ga distance in GaAs(2.45A). No detectable relaxation is observed in the P second and third atomic shells. In Sdoped GaAs we find two different populations of S-Ga bonds with nearly equal intensity and both with S located on the As sub-lattice. These findings indicate two different configurations of substitutional S in GaAs. The coexistence of two similarly populated, charge compensating configurations is the first structural evidence which allows us to explain the observation that in n-doped GaAs the electrical activity of donors is lower than the atomic concentration. Finally, we present experimental results on S impurities in AlxGa1-xAs (0.2

The Effect of Rapid Thermal Treatment on the Structural and Optoelectronic Properties of Epitaxial Gaas on Si Grown With or Without Ge Intermediate Layers

Abstract: Characteristics of MOCVD GaAs grown on Si are compared before and after a rapid thermal treatment. The GaAs-on-Si samples were prepared both with and without a Ge intermediate layer, which is used to accomodate mismatches of lattice, thermal and chemical origin between GaAs and Si. Structural, interfacial, chemical, and electrical changes have been examined. RBS and Raman characterization showed improvement of GaAs crystallinity after RTA. In most cases, the interfaces were found to become sharper after RTA, but chemical interdiffusion was observed to cause some effect on the structural and electrical properties. For gold-contacted GaAs, RTA seems to degrade the electrical and optoelectronic properties via gold interdiffusion into GaAs. Comparative studies of the GaAs/Si and GaAs/Ge/Si samples suggests that the two respond somewhat differently to RTA.