Samseok Jang

Influence of the Density of Crack-Initiating Defects on Crack Spacing for GaN Films on Si(111) Substrate

This study examines the cracking of GaN films grown on Si(111) substrates, with particular focus on the effect of the density of crack-initiating defects (CIDs) on the crack spacing. The relationship between the CID density and crack spacing was examined by comparing specimens of the same thickness and under the same stress but with different CID density. The CID density in the GaN layer was changed by varying the ion-implanted area using patterning prior to metal–organic chemical vapor deposition (MOCVD) growth. The crack spacing decreased with increasing CID density, but this effect could not be explained by the previous model. Therefore, a CID-density related factor, nd, was newly introduced to explain the crack spacing and film stress relationship.

Study of a-Plane GaN Epitaxial Lateral Overgrowth Using Carbonized Photoresist Mask on r-Plane Sapphire

Epitaxial lateral overgrowth (ELO) a-plane GaN samples were successfully grown on masked sapphire (102) substrates using an in-situ carbonized photoresist (PR) mask by a metalorganic chemical vapor deposition (MOCVD) method. The PR masks for the ELO process were prepared using conventional lithography in the form of a stripe with an opening of 4 µm and a period of 12 µm. The stripe-patterned PR was annealed at 1100 °C in a H2 atmosphere. The stripes were aligned parallel to the GaN direction. The ELO process of GaN was strongly dependent on the direction of the stripes. Overall, the PR masks on the r-plane sapphire substrate were carbonized during the heating step before the main growth, so that the carbonized PR mask acted as an ELO mask. The study results confirmed the promising potential of the ELO process using an in-situ carbonized PR mask on r-plane sapphire.

In situ Monitoring of Target Voltage in Magnetron Reactive Sputtering of ZnO

Zinc oxide (ZnO) films were deposited on glass substrates by radio-frequency (RF) magnetron reactive sputtering at room temperature. With the relationship between deposition rate and oxygen flow, the appropriate deposition condition was not set up easily for reactive sputtering. The mechanisms between the sputtered material and the reactive gas may cause some processing stability problems. Therefore, it is required to find the in situ way of determining which mode films would be deposited before deposition. The in situ monitoring of the target voltage during deposition can be helpful for obtaining transparent and conductive films. With the in situ monitoring of the target voltage, the properties of ZnO thin films can be predicted and selected within metallic, transition, and oxide modes.