A Study of Piezoelectric Field Related Strain Difference in GaN-Based Blue Light-Emitting Diodes Grown on Silicon(111) and Sapphire Substrates.

We investigate the strain difference in InGaN/GaN multiple quantum wells of blue light-emitting diode (LED) structures grown on silicon(1 11) and c-plane sapphire substrates by comparing the strength of piezo-electric fields in MQWs. The piezo-electric fields for two LED samples grown on silicon and sapphire substrates are measured by using the reverse-bias electro-reflectance (ER) spectroscopy. The flat-band voltage is obtained by measuring the applied reverse bias voltage that induces a phase inversion in the ER spectra, which is used to calculate the strength of piezo-electric fields. The piezo-electric field is determined to be 1.36 MV/cm for the LED on silicon substrate and 1.83 MV/cm for the LED on sapphire substrate. The ER measurement results indicate that the strain-induced piezo-electric field is greatly reduced in the LED grown on silicon substrates consistent with previous strain measurement results by micro-Raman spectroscopy and high-resolution transmission electron microscopy.

Comparison of Strain in GaN-Based Blue Light-Emitting Diode Grown on Silicon(111) and Sapphire Substrates.

We compare the strain states and device performances of GaN-based blue light-emitting diodes (LEDs) grown on Si(111) and sapphire substrates. The strain characteristics are investigated using micro-Raman spectroscopy and high-resolution transmission electron microscopy. These analyses reveal that GaN layer grown on Si has a residual tensile strain in contrast to a compressive strain for GaN on sapphire, and quantum wells (QWs) on GaN/Si experience reduced lattice mismatch than those of GaN/sapphire. When external quantum efficiencies of LED on sapphire and Si substrates are compared, the LED on Si shows better efficiency droop characteristics and this is attributed to a decrease in piezo-electric field strength in InGaN/GaN layers owing to reduced lattice mismatch.

Hematobilia from ruptured hepatic artery aneurysm. Report of two cases.

Hematobilia secondary to hepatic artery aneurysm must be considered in the differential diagnosis of unexplained gastrointestinal tract hemorrhage. We treated two patients with ruptured hepatic artery aneurysm. One had hepatic artery aneurysm proximal to the gastroduodenal artery; the other had an intrahepatic pseudoaneurysm in the right lobe of the liver. The first patient was treated with obliterative endoaneurysmorrhaphy. The second required ligation of feeding vessels, cholecystectomy, and reconstruction of cholecystoduodenal fistula.

Experience with and complications of postoperative choledochofiberscopy for retained biliary stones.

Biliary calculi retained after choledochotomy were removed from 66 patients by means of the Olympus fiberoptic choledochoscope via a T-tube tract. The stones were lodged in the common bile duct in 18 of the patients and in the intrahepatic ducts in 48 patients. Complete removal of the retained stones was achieved from the common bile duct in 16 cases and from the intrahepatic ducts in 38. No further measures were necessary in these patients. The complication rate of choledochofiberscopy was low. Of the total 218 endoscopies, 8 were followed by abdominal pain, 6 by chills and fever and 2 by bleeding from the fistula tract. A duodenocutaneous fistula developed in one patient. Postoperative choledochofiberscopy is a useful and effective method for the management of retained biliary calculi.