Uniformity investigation of MOCVD‐grown LED layers page 30–40 Haisheng Fang et al.

Abstract

The image shows a graphite susceptor, on which GaN wafers were grown. Uniformity of the produced wafers is at the heart of high‐power‐LED industries. The main purpose of the paper is to propose a direction to optimize the MOCVD reactors by comprehensively analyzing uniformities of the wafers. To achieve this goal, growth of GaN compounds in a specific MOCVD reactor, capable of a one‐time production of 36 × 2″ wafers of nitrides, has been investigated. To examine growth uniformity across a wafer and from wafer to wafer, the reactor is divided into Zone A, Zone B and Zone C according to distance to the center of the graphite susceptor. Comparative analysis of each zone offers a straightforward view of the mean excitation wavelength, luminous intensity, film thickness and their standard deviations. Conformity of the growth uniformity in each zone is further checked carefully through averaging across‐wafer and wafer‐to‐wafer variables and their standard deviations. Zone B is found to retain excellent wavelength uniformity, since it is located at the middle of the susceptor with weaker effects of the susceptor edge and of the inlet gas flow. Zone A, at the center of the reactor, has the best mean intensity and thickness uniformities due to a well control of the infrared temperature measurement during the growth. Zone C is the worst in the uniformities, and should be the main focus when optimizing the reactor. The above experimental analysis reveals the principles common to the MOCVD technique, and provides a basic for further optimization of the process window to improve the cycles with considerable reduction of the costs. (Picture: Haisheng Fang et al., pp. 30–40, in this issue)

The Diminishing Role of Whole-Brain Radiation Therapy in the Treatment of Brain Metastases

“…In that regard, multiple studies have demonstrated the intracranial activity of inhibitors for EGFR , ALK , and BRAF . As for immunotherapy, a retrospective study from MD Anderson in patients with melanoma with 4 or more BrM given ipilimumab and SRS found better intracranial control than a propensity-matched cohort who received WBRT, suggesting that that anti- CTLA4 has similar or better ability to control microscopic disease in the brain.…”