Engineering of impact ionization characteristics in In0.53Ga0.47As/Al0.48In0.52As superlattice avalanche photodiodes on InP substrate.

We report on engineering impact ionization characteristics of In0.53Ga0.47As/Al0.48In0.52As superlattice avalanche photodiodes (InGaAs/AlInAs SL APDs) on InP substrate to design and demonstrate an APD with low k-value. We design InGaAs/AlInAs SL APDs with three different SL periods (4 ML, 6 ML, and 8 ML) to achieve the same composition as Al0.4Ga0.07In0.53As quaternary random alloy (RA). The simulated results of an RA and the three SLs predict that the SLs have lower k-values than the RA because the electrons can readily reach their threshold energy for impact ionization while the holes experience the multiple valence minibands scattering. The shorter period of SL shows the lower k-value. To support the theoretical prediction, the designed 6 ML and 8 ML SLs are experimentally demonstrated. The 8 ML SL shows k-value of 0.22, which is lower than the k-value of the RA. The 6 ML SL exhibits even lower k-value than the 8 ML SL, indicating that the shorter period of the SL, the lower k-value as predicted. This work is a theoretical modeling and experimental demonstration of engineering avalanche characteristics in InGaAs/AlInAs SLs and would assist one to design the SLs with improved performance for various SWIR APD application.

Variation of blood pressure during topical phacoemulsification.

BACKGROUND: The changes of blood pressure in patients undergoing cataract procedure are not well studied. The blood pressures of cataract patients often become uncontrolled intraoperatively causing the procedure to be postponed. Intraoperative rise in blood pressure has been associated with ocular complications such as suprachoroidal haemorrhage and can be fatal from stroke or even myocardial infarction. We attempt to study the changes in blood pressure of patients undergoing cataract surgery. AIM: Prospective study on the variation of blood pressure pre- and intra-operatively. METHOD: The blood pressure readings of patients going for cataract procedures were measured in five stages during the pre-assessment clinic, on arrival at the day surgery, at the anaesthetic room, on the operating table intraoperatively; and postoperatively. The readings were compared to their age, sex, past medical history, and use of antihypertensive medication. RESULTS: The rise in systolic blood pressures between intraoperative readings and those at the preassessment and anaesthetic room was highly statistically significant.Being older (>65 years of age), taking more than two antihypertensive drugs, being hypertensive, or having a family history of hypertension does not appear to increase the risk. CONCLUSION: Our study showed that there is a significant rise in systolic blood pressures especially in females during topical phacoemulsification. Further studies are needed on the factors that determine this increase and the changes in blood pressures during different stages of the procedure.

Descemetocoele from exposure keratopathy.

We present a case of descemetocoele secondary to facial nerve palsy causing exposure keratopathy. To prevent further ocular morbidity, a central tarsorrhaphy was performed. On follow-up two weeks later, no further deterioration of the eye was detected.

Chest radiographs in uveitis patients.

This is an article regarding a patient presented with bilateral uveitis who was subsequently found to have lung carcinoma on further investigations. We recommend doing a CXR especially in uveitis patients who have a history of smoking.