Developments of GaN Bulk Substrates for GaN Based LEDs and LDs
In the present work, we discuss the importance of bulk GaN substrates for GaN based LEDs and LDs. As crystal growth methods for growing bulk GaN, we study the hydride vapor phase epitaxial (HVPE) method and the pressure-controlled solution growth (PC-SG) method. The recent results obtained by these two methods are presented. The maximum size of the grown single crystals was 3 × 4 cm2 for the HVPE method and 12 mm diameter for the PC-SG method. Both methods can provide high quality GaN substrates, with a low dislocation density of the level of less than 106 cm–2.
InGaN-based LEDs and laser diodes
A violet InGaN multi-quantum well/GaN/AlGaN separate- confinement-heterostructure laser diode (LD) was grown on epitaxially laterally overgrown GaN on sapphire. The threshold current density was 2 - 4 kA/cm2. The LDs with cleaved mirror facets showed an output power as high as 30 mW under room-temperature continuous-wave (CW) operation. The stable fundamental transverse mode in the near-field patterns was observed at an output power up to 30 mW. The lifetime of the LDs at a constant output power of 5 mW was more than 1,900 hours under CW operation at an ambient temperature of 50 degree(s)C.
A controlled, randomized trial of highly selective vagotomy versus selective vagotomy and pyloroplasty in the treatment of duodenal ulcer.
The results of highly selective vagotomy without drainage and selective vagotomy with pyloroplasty for duodenal ulcer were compared in a randomized, controlled trial of a series of 100 patients. The frequency of dumping, diarrhoea, and epigastric fullness was significantly lower after highly selective (6, 6, and 8 percent) than after selective vagotomy (30, 20, and 28 percent) one year after the operations. Recurrent and persisting duodenal ulcers appearing from one to four years after the operations were significantly more frequent after highly selective (22 percent) than after selective vagotomy (8 percent). No significant relationships were found between recurrent ulceration and gastric acid secretion measurements after the two operations. The Hollander response was early positive in 28 percent and late positive in 30 percent of the patients subjected to highly selective vagotomy, while the corresponding figures after selective vagotomy were 26 and 32 percent. The overall clinical results of the two operations were not different according to the classification of Visick. Excluding the patients with recurrence resulted in significantly better clinical results after highly selective vagotomy.