ANALYSIS OF STEP-VELOCITY DEPENDENCES OF CARBON CONCENTRATION IN c- AND m-PLANE GaN HOMOEPITAXIAL LAYERS

Reported step-velocity dependences of carbon concentration in c- and m-plane GaN homoepitaxial layers were successfully reproduced based on a step-edge segregation model with the following assumptions: 1) the diffusion coefficient of carbon in GaN is 2×10^-13 cm^2/s (@ 1000℃−1100℃); 2) the length of time before the carbon concentration at the step-edge site reaches its equilibrium value is sufficiently shorter than the meantime until a carbon atom incorporated at the kink site moves through the step-edge site to the surface site

ESTIMATION OF EXCITATION DENSTITY OF REPORTED TWO-PHOTON PHOTOLUMINESCENCE INTENSITY DISTRIBUTIONS AT A DISLOCATION IN AN n-GaN LAYER ON A M-3D SUBSTRATE

We estimated the excitation density of the reported two-photon photoluminescence from an n-GaN layer on an M-3D substrate by fitting the intensity distributions at a dislocation. We found that all the data points of the intensity distributions were reproduced with the effective dislocation radius of 8 nm. Considering the range of the excess hole concentration (Δp) within which almost all data points fell, we estimated Δp to be 10^16±1 cm^−3

Piezoelectric properties of microfabricated (K,Na)NbO3 thin films

A novel microfabrication method of lead-free piezoelectric sodium potassium niobate [(K, Na)NbO3, KNN] thin films was proposed, and the piezoelectric characteristics of the KNN microactuators were evaluated. The KNN thin films were directly deposited on microfabricated Si microcantilevers. The transverse piezoelectric coefficient d31 of the KNN films was calculated as −53.5 pm/V at 20 Vpp from the tip displacement of the microcantilevers. However, the tip displacement showed large electric-field dependence because of the extrinsic piezoelectric effect, and the intrinsic piezoelectric effect of the KNN microcantilevers was smaller than that of KNN on unprocessed thick substrates. In contrast, the extrinsic piezoelectric effect was almost independent of the microfabrication of the KNN films

Effect of Inductively Coupled Plasma Etching in p-Type GaN Schottky Contacts

The effects of inductively coupled plasma (ICP) etching damage on the electrical characteristics of low-Mg-doped p-GaN Schottky contacts were evaluated. The ICP etching greatly reduced the memory effect in the current-voltage characteristics and the difference between the depletion layer capacitances before and after forward current injection. These reductions indicate that acceptor-type interfacial defects were passivated by H atoms during ICP etching. Additionally, photoresponse (PR) measurements revealed that Schottky barrier height was increased from 2.08 to 2.63 eV by the etching. Because of the surface state change, the Fermi level position would be moved toward the conduction band edge slightly by the etching. After annealing, the memory effect and the capacitance change were partially restored, and the PR spectra showed less variation. Absorbed H atoms on the p-GaN surface might be released by annealing.本著作物の著作権は公益社団法人応用物理学会に帰属します。/公益社団法人応用物理学会 2013/ 2013 The Japan Society of Applied Physic

High-k Dielectric Passivation for GaN Diode with a Field Plate Termination

Vertical structured Gallium nitride (GaN) p-n junction diodes with improved breakdown properties have been demonstrated using high-k dielectric passivation underneath the field plate. Simulation results at a reverse voltage of 1 kV showed that the maximum electric field near the mesa-etched p-n junction edges covered with film of dielectric constant k = 10 was reduced to 2.0 MV/cm from 3.0 MV/cm (SiO2 (k = 3.9)). The diodes were fabricated using the high-k mixed oxide of SiO2 and CeO2 with k = 12.3. I–V characteristics of the diode with a field plate showed a breakdown voltage above 2 kV with an increased avalanche resistance. This means that the electric field reduces at the periphery of the mesa-etched p-n junction and is uniformly formed across the whole p-n junction. It is clear that high-k dielectric film passivation and filed plate termination are essential techniques for GaN power devices

Photoelectrochemical Etching Technology for Gallium Nitride Power and RF Devices

Photoelectrochemical (PEC) etching was used to fabricate deep trench structures in GaN-on-GaN epilayers grown on n-GaN substrates. The width of the side etching was less than 1 mu m, with high accuracy. The aspect ratio (depth/width) of a 3.3-mu m-wide trench with a PEC etching depth of 24.3 mu m was 7.3. These results demonstrate the excellent potential of PEC etching for fabricating deep trenches in vertical GaN devices. Furthermore, we simplified the PEC etching technology to permit its use in a wafer-scale process. We also demonstrated simple contactless PEC etching technologies for the manufacture of power and RF devices. A trench structure was fabricated in a GaN-on-GaN epilayer by simple contactless PEC etching. The role of the cathodic reaction in contactless PEC etching is discussed in relation to the application of a GaN HEMT epilayer on a semi-insulating substrate. Fortunately, the GaN HEMT structure contains an ohmic electrode that can act as a cathode in contactless PEC etching, thereby permitting the recess etching of a GaN HEMT epilayer grown on a semi-insulating SiC substrate. These results indicate that PEC etching technologies are becoming suitable for use in the fabrication of practical GaN power and RF devices

CE-MS-Based Identification of Uremic Solutes Specific to Hemodialysis Patients

Uremic toxins are suggested to be involved in the pathophysiology of hemodialysis (HD) patients. However, the profile of uremic solutes in HD patients has not been fully elucidated. In this study using capillary electrophoresis mass spectrometry (CE-MS), we comprehensively quantified the serum concentrations of 122 ionic solutes before and after HD in 11 patients. In addition, we compared the results with those in non-HD patients with chronic kidney disease (CKD) to identify HD patient-specific solutes. We identified 38 solutes whose concentrations were higher in pre-HD than in CKD stage G5. Ten solutes among them did not significantly accumulate in non-HD CKD patients, suggesting that these solutes accumulate specifically in HD patients. We also identified 23 solutes whose concentrations were lower in both pre- and post-HD than in CKD stage G5. The serum levels of 14 solutes among them were not affected by renal function in non-HD patients, suggesting that these solutes tend to be lost specifically in HD patients. Our data demonstrate that HD patients have a markedly different profile of serum uremic solute levels compared to that in non-HD CKD patients. The solutes identified in our study may contribute to the pathophysiology of HD patients