K. A. Jones

High quality crystalline ZnO buffer layers on sapphire (001) by pulsed laser deposition for III–V nitrides

ZnO thin films with near perfect crystallinity have been grown epitaxially on sapphire (001) by pulsed laser deposition technique. The ω-rocking curve full width at half-maximum of the ZnO(002) peak for the films grown at 750 °C, oxygen pressure 10−5 Torr was 0.17°. The high degree of crystallinity was confirmed by ion channeling technique providing a minimum Rutherford backscattering yield of 2%–3% in the near-surface region (∼2000 A). The atomic force microscopy revealed smooth hexagonal faceting of the ZnO films. It has been possible to deposit epitaxial AlN films of thickness 1000 A on epi-ZnO/sapphire. Excellent crystalline properties of these epi-ZnO/sapphire heterostructures are, thus, promising for lattice-matched substrates for III–V nitride heteroepitaxy and optoelectronics devices.

Growth of epitaxial GaN films by pulsed laser deposition

High crystalline quality epitaxial GaN films with thicknesses 0.5–1.5 μm have been successfully grown directly on Al2O3(0001) substrate by pulsed laser deposition (PLD). For films grown at 950 °C, we obtained an x-ray diffraction rocking curve linewidth of 7 arc min. The ion channeling minimum yield in the near-surface region (∼2000 A) for a 0.5 μm thick film was ∼3%–4% indicating a high degree of crystallinity. The optical absorption edge measured by UV-visible spectroscopy was sharp, and the band gap was found to be 3.4 eV. The crystalline properties of these PLD GaN films are comparable to those grown by metalorganic chemical vapor deposition and molecular beam epitaxy.

Activation of ion implanted Si in GaN using a dual AlN annealing cap

A dual annealing cap composed of a thin, low temperature metal-organic chemical vapor deposition (MOCVD) deposited AlN adhesion layer and a thicker, sputtered AlN film for added mechanical strength enabled us to anneal Si-implanted layers for 30 min at temperatures up to 1250 °C. At higher temperatures the cap was destroyed by the large partial pressure of the N2 from the GaN, which exceeds the yield strength of AlN. Electrical activations as high as 70% and electron mobilities comparable to those of in situ doped films were achieved. Compared to other methods, the surfaces are better protected using this cap because it adheres better than sputtered AlN, SiO2, or Si3N4; does not crack like MOCVD grown AlN films deposited at normal temperatures (∼1100 °C); and is stronger than thin MOCVD grown AlN films deposited at low temperatures (∼600 °C). Even though N does not escape, and in so doing, forms thermal etch pits, the surface of the annealed GaN is roughened by solid state diffusion with the surface rough...

Ohmic metallization technology for wide band-gap semiconductors

Ohmic contact metallizations on p-type 6H-SiC and n-type ZnO using a novel approach of focused ion beam (FIB) surface-modification and direct-write metal deposition will be reviewed, and the properties of such focused ion beam assisted non-annealed contacts will be reported. The process uses a Ga focused ion beam to modify the surface of the semiconductor with different doses, and then introduces an organometallic compound in the Ga ion beam, to effect the direct-write deposition of a metal on the modified surface. Contact resistance measurements by the transmission line method produced values in the low 10−4 Ω cm2 range for surface-modified and direct-write Pt and W non-annealed contacts, and mid 10−5 Ω cm2 range for surface-modified and pulse laser deposited TiN contacts. An optimum Ga surface-modification dosage window is determined, within which the current transport mechanism of these contacts was found to proceed mainly by tunneling through the metal–modified–semiconductor interface layer.

Effectiveness of AlN encapsulant in annealing ion-implanted SiC

Aluminum nitride (AlN) has been used as an encapsulant for annealing nitrogen (N), arsenic (As), antimony (Sb), aluminum (Al), and boron (B) ion-implanted 6H-SiC. Atomic force microscopy has revealed that the AlN encapsulant prevents the formation of long grooves on the SiC surface that are observed if the AlN encapsulant is not used, for annealing cycles up to 1600 °C for 15 min. Secondary ion mass spectrometry measurements indicated that the AlN encapsulant is effective in preserving the As and Sb implants, but could not stop the loss of the B implants. Electrical characterization reveals activation of N, As, Sb, and Al implants when annealed with an AlN encapsulant comparable to the best activation achieved without AlN.

Fabrication and characterization of epitaxial AlN/TiN bilayers on sapphire

Abstract We have grown high quality AlN/TiN heterostructures on sapphire (0001) substrates using the pulsed laser deposition (PLD) technique. The X-ray diffraction studies revealed that the AlN (0002) and TiN (111) planes were parallel to the sapphire (0006) plane and the rocking curve full widths at half maximum (FWHM) were 0.2°–0.3° for these layers. The AlN/TiN interface was found to be sharp from secondary ion mass spectrometry (SIMS) studies. The electrical resistivity of the epitaxial TiN buffer layer was as low as 14 μΩ cm at room temperature, indicating that TiN could be an excellent contact material for nitride based wide bandgap semiconductor devices. The reflection spectrophotometry measurements showed that the AlN layer deposited on top of the TiN buffer retained its bulk optical properties having a refractive index of 2.25 and an energy gap larger than 5.9 eV. The electrical transport across the TiN/AlN/TiN capacitor could be explained with the ionic conduction model.

Advances in pulsed laser deposition of nitrides and their integration with oxides

Abstract Pulsed laser deposition (PLD) is emerging as the fastest thin film prototyping tool for a variety of multicomponent ceramic films. There could be significant payoffs in applying this technique for the growth of GaN and related wide bandgap semiconductor films and heterostructures (primarily for their potential applications in optoelectronics and high-temperature high-power electronics), on account of PLDs speed and flexibility. The present work describes the pulsed laser deposition of GaN and other participating electronic and optoelectronic materials such as AlN, TiN, and ZnO on sapphire. A pulsed KrF excimer laser was used for ablation of the sintered stoichiometric GaN, AlN, and TiN targets. The processing parameters such as laser fluence, substrate temperature, background gas pressure, and pulse repetition rate have been optimized for growth of high-quality epitaxial films. The films were characterized by X-ray diffraction, Rutherford backscattering spectrometry, ion channeling, high-resolution transmission electron microscopy, atomic force microscopy, UV–visible spectroscopy, and electrical resistivity measurement. We also discuss pulsed laser deposition of multilayer heterostructures of TiN/AlN/TiN (as capacitors for high-temperature electronics), ZnO heteroepitaxy and its integration with GaN for fabrication of novel devices.

AlN as an encapsulate for annealing SiC

AlN films grown by either organometallic vapor phase epitaxy (OMVPE) or pulsed laser deposition (PLD) can be used to encapsulate SiC when heated in an argon atmosphere at temperatures at least as high as 1600 °C for times at least as long as 30 min. The coverage of the AlN remains complete and the AlN/SiC interface remains abrupt as determined by Auger electron spectroscopy. However, considerable atomic movement occurs in the AlN at 1600 °C, and holes can form in it as the film agglomerates if there are large variations in the film thickness. Also, the SiC polytype near the surface can in some instances be changed possibly by the stress generated by the epitaxial AlN film. Using x-ray diffraction measurements, we also found that, during the 1600 °C anneal, grains with nonbasal plane orientations tended to grow at the expense of those with basal plane orientations in the OMVPE films, whereas grains with only the basal plane orientation tended to grow in the PLD films. However, there is no indication that t...

Annealing ion implanted SiC with an AlN cap

Abstract An AlN cap was used to try to prevent the preferential evaporation of Si during the high temperature anneals required to activate N implanted into a SiC substrate. The process was essentially successful as the electrical measurements showed that the resistivity continued to decrease with increasing annealing temperatures up to 1600°C and times up to 120 min. The changes were, however, marginal when compared to a 1500°C, 30 min anneal suggesting that this anneal would be sufficient to activate most of the N implants. There is evidence for a small amount of Si being lost near the surface. This could occur where the AlN pulled away locally from the SiC wafer; this effect was stronger for patterned substrates where stress concentrations can occur at steps. For the most part, however, the SiC surface retained its integrity even during the process of removing the AlN film with a hot KOH etch. Also, there was no evidence that Al from the AlN contaminated the N implanted region by diffusing in during the anneals. The surface of the AlN retained its integrity during the anneal although topographical changes suggested that considerable atomic motion had occurred. This coincided with the formation of an amorphous AlN layer in the film.

Deep-level transient spectroscopy study on double implanted n+–p and p+–n 4H-SiC diodes

Planar n+–p and p+–n junction diodes, fabricated in 4H-SiC epitaxial layers using a double-implantation technology (a deep-range acceptor followed by a shallow-range donor implantation and vice versa), are characterized using capacitance deep-level transient spectroscopy (DLTS) to detect deep levels, which may influence device electrical performance. Either Al or B was used as the acceptor, while N or P was used as the donor, with all implants performed at 700 °C and annealed at 1600–1650 °C with an AlN protection cap. Different traps were observed for the various dopants, which are believed to be related to different impurity-defect complexes. A trap at ∼EV+0.51 eV was observed in nitrogen-implanted samples, while an acceptor trap at ∼EV+0.28 eV and a donor trap at ∼EC−0.42 eV were observed in Al-implanted samples. A prominent boron-related D-center trap at ∼EV+0.63 eV is seen in the DLTS spectra of B-implanted diodes. In diodes with implanted phosphorus, three traps at ∼EV+0.6 eV, EV+0.7 eV, and EV+0.92...