Very high external quantum efficiency and wall-plug efficiency 527 nm InGaN green LEDs by MOCVD.

We demonstrate very high luminous efficacy InGaN-based green light-emitting diodes (LEDs) grown on c-plane patterned sapphire substrates (PSS) using metal organic chemical vapor deposition (MOCVD). The 527 nm green LEDs show a peak external quantum efficiency (EQE) of 53.3%, a peak wall-plug efficiency (WPE) of 54.1% and a peak luminous efficacy of 329 lm/W, respectively. A high EQE of 38.4%, a WPE of 32.1% and a very low forward voltage of 2.86 V were obtained at a typical working current density of 20 A/cm2. By operating low cost green LEDs at a low current density, our devices (0.5 mm2) demonstrating an EQE and a WPE higher than 50% and an efficacy of 259 lm/W at 4 A/cm2 with an output power of 24 mW. High crystal quality of the InGaN/GaN MQWs was characterized by X-ray diffraction (XRD) and the advantage of the epitaxy design was investigated by APSYS software simulation. These results provide a simple way to achieve very high efficiency InGaN green LEDs.

[Particle induced X-ray emission for trace element analysis of hairs from patients with cancer].

In this paper, trace element analysis of the hairs from the patients with nasopharyngeal carcinoma (NPC) and osteoma was made using particle induced X-ray emission (PIXE) technique in order to obtain some information on the correlation between trace element and these two tumors. The hair samples of 34 NPC patients were each collected before and three months after radiotherapy (60Co) (group 1). The hair specimens from 34 osteoma patients were collected preoperatively and postoperatively. For comparison, 65 hair samples were collected from 40 normal subjects (group 2) and 25 NPC patients, who had received radiotherapy (60Co) five years before without any recrudescence (group 3). The trace element analysis of all specimens was made by PIXE. The results show that there is a significant difference between groups 1 and 2 (P less than 0.01) but no difference is found between groups 2 and 3 for Mn, Cu, Zn, As etc. content in the hairs. Cu and Zn content in the hairs of the osteoma patients is much lower than that of the normal subjects (P less than 0.01) while for K, Ti and Mn content, the former is higher than the latter. The above experimental results are discussed in detail.