Two-step surface treatment is introduced to obtain low resistance Pt contacts to p-type GaN. The first step is performed after the mesa etching process using buffered oxide etch ͑BOE͒ and ammonium sulfide ͓(NH 4 ͒ 2 S x ͔. This is followed by the second step using BOE. The Pt contact, that was simply BOE treated, yields 2.1(Ϯ0.9)ϫ10 Ϫ2 ⍀ cm 2. However, the contact which was treated sequentially using ultrasonically boiled BOE ͑10 min͒ and boiled (NH 4 ͒ 2 S x ͑10 min͒, produces a specific contact resistance of 2.0(Ϯ3.5)ϫ10 Ϫ5 ⍀ cm 2. To the best of our knowledge, this is the lowest contact resistance reported hitherto for the contacts on p-GaN. The effective Schottky barrier heights ͑SBHs͒ of the differently surface-treated contacts were determined using the Norde and current-voltage methods. It is shown that the SBHs are dependent upon the surface treatment conditions.

X-ray photoelectron spectroscopy (XPS) was employed to investigate the chemical bonding and electronic properties of the interfaces between Pt and p-GaN layers that were two-step surface treated using a buffered-oxide etch solution, and hence, to understand the surface-treatment time dependence of the Schottky barrier height (SBH). Current–voltage (I–V) measurements show that the effective SBH decreases with increasing surface-treatment time. The XPS results show that as the treatment time increases, the Ga 2p and Pt 4f core levels for the 20-min-treated samples shift toward the lower-binding-energy side by 0.6 and 1.5 eV, respectively, compared to the 0.5-min-treated one. It is further shown that the intensity of the oxygen core-level peak decreases with increasing treatment time. Based on the I–V and XPS results, the observed reduction of the effective SBHs is attributed to the combined effects of the effective removal of the native oxide and the shift of the surface Fermi level toward the valence-band edge.

In this study, the atomic layer etching characteristics and the etch mechanism of ͑100͒ InP as functions of Cl 2 pressure and Ne neutral beam irradiation dose were investigated. When Cl 2 pressure and Ne neutral beam irradiation dose were lower than the critical values of 0.4 mTorr and 7.2 ϫ 10 15 at./ cm 2 cycle, respectively, the InP etch rate ͑Å/cycle͒ and the InP surface roughness varied with Cl 2 pressure and Ne neutral beam irradiation dose. However, when the Cl 2 pressure and Ne neutral beam irradiation dose were higher than the critical values, the InP etch rate remained as 1.47 Å / cycle, corresponding to one monolayer per cycle, and the surface roughness and the surface stoichiometry remained similar to those of InP before etching.

Schottky barrier behaviors of Pt contacts to n-InGaN have been investigated by means of current-voltage (I-V) and capacitance-voltage (C-V) methods. It is found that the Schottky barrier heights (SBHs) determined by thermionic emission (TE) and thermionic field emission (TFE) modes using the I-V data are quite different from each other. However, the SBHs obtained by the TFE mode are fairly similar to theoretically calculated values, which are in good agreement with the results obtained by the C-V method. It is also shown that the SBHs and the ideality factors calculated by the TE and TFE modes decrease with increasing annealing temperature. The different SBHs obtained by the TE and TFE modes, the annealing temperature dependence of the SBHs, and the ideality factors are described and discussed in terms of the presence of different types of native point defects near the InGaN surface.

We report on a promising metallization scheme for high-quality Ohmic contacts to surface-treated p-GaN:Mg (2 -3ϫ10 17 cm Ϫ3 ). It is shown that the as-deposited Pt/Ru contact produces a specific contact resistance of 7.8(Ϯ2.2)ϫ10 Ϫ4 ⍀ cm 2 . However, annealing of the contact at 600°C for 2 min results in a resistance of 2.2(Ϯ2.0)ϫ10 Ϫ6 ⍀ cm 2 . It is also shown that the light transmittance of the annealed contact is 87.3% at 470 nm. Furthermore, the surface of the contact annealed at 600°C for 30 min is found to be very smooth with a rms roughness of 0.8 nm. These results strongly indicate that the Pt/Ru can be a suitable scheme for the fabrication of high-performance laser diodes or other devices.

We report on the electronic transport mechanisms for nonalloyed Pt Ohmic contacts to p-GaN which were surface treated using a buffered oxide etch solution and (NH4)2Sx. Measurements show that the value of the effective Richardson constant (A**) is 12 A cm−2 K−2, which is considerably smaller than the theoretical value of 103.8 A cm−2 K−2. Based on Hall-effect results, the two-step surface-treated contact is modeled to consist of a Pt/p+-/p-GaN structure, and the conventionally treated contact consists of a Pt/p-GaN structure. The theoretical results obtained using these models are compared with the experimental data. It is shown that for the conventionally treated contact thermionic emission dominates the current flow, whereas for the two-step surface-treated contact, field emission is dominant.

We report on a Pt ͑20 nm͒ Ni ͑30 nm͒/Au ͑80 nm͒ metallization scheme for low-resistance ohmic contacts to the moderately doped p-type GaN:Mg (3ϫ10 17 cm Ϫ3). Both as-deposited and annealed Pt/Ni/Au contacts on p-GaN exhibit linear current-voltage characteristics, showing that a high-quality ohmic contact is formed. The Pt/Ni/Au scheme shows the specific contact resistance of 5.1ϫ10 Ϫ4 ⍀ cm 2 when annealed at 350°C for 1 min in a flowing N 2 atmosphere.

We have demonstrated self-catalyzed GaNxP1−x and GaNxP1−x/GaNyP1−y core/shell nanowire growth by gas-source molecular beam epitaxy. The growth window for GaNxP1−x nanowires was observed to be comparable to that of GaP nanowires (∼585 °C to ∼615 °C). Transmission electron microscopy showed a mixture of cubic zincblende phase and hexagonal wurtzite phase along the [111] growth direction in GaNxP1−x nanowires. A temperature-dependent photoluminescence (PL) study performed on GaNxP1−x/GaNyP1−y core/shell nanowires exhibited an S-shape dependence of the PL peaks. This suggests that at low temperature, the emission stems from N-related localized states below the conduction band edge in the shell, while at high temperature, the emission stems from band-to-band transition in the shell as well as recombination in the GaNxP1−x core.