Light-emitting diodes (LEDs) are solid-state semiconductor devices that contain p – n junctions. White LEDs have attracted much attention for display technology and offer significant energy savings. Currently, the main method of fabricating commercial white LEDs is to combine blue LED with embedded yellow phosphors. However, nitride-related materials used in the blue LEDs experience an efficiency drop in the yellow region due to the lattice defects and low crystal quality. Arsenide/phosphide-alloy materials used in the red LED also lose efficiency in yellow region because their bandgap is indirect. My research aims to solve the efficiency gap in yellow-green region by using selective-area growth. Wurtzite (WZ) AlInP is a candidate material because its bandgap changes to direct from indirect owing to the crystal phase transition from zincblende (ZB) to WZ. Nanowire (NW) structure offers convenient approach to control the crystal phase transition by properly varying growth parameters such as growth temperature, V/III ratio and doping amount. With the completion of my work, true white LEDs with high-efficiency will become reality and promise the active potential for enormous energy savings.

We hold a meeting every Monday. In these meetings, everyone needs to give a small talk with slides to report their research progress. The frequency of report varies depending on the academic year, for example PhD students are required to present their work once a week, while Master students need to give presentations once every two weeks. During the report, we usually summarize our experiment results and discuss with professors and colleagues. And after attending any conferences, we need to give a short report to share research we’re interested in, which is a good way to keep us up to date on the recent progress. It’s not an official meeting, so everyone can share their opinions or ask questions freely. The weekly meeting is also a great opportunity to learn about other researches you’re not familiar with!

We have a clean room where we conduct almost all our experiments. Each machine belongs to a different laboratory, but students who don’t belong to that laboratory can still use them if they get permission. In our laboratory, we apply sputter, electron beam lithography (EB), reactive ion etching (RIE), metal-organic vapor-phase epitaxy (MOVPE) and other equipment for our epitaxial growth. We’re able to carry out the whole experiment from substrate preparation to crystal growth by ourselves once we’re familiar with those machines. Members in our group teach new members how to use those machines carefully and patiently. Except for crystal growth experiments, we also fabricate devices such as LEDs and assess their electronic properties. We have the freedom to arrange our experiment schedule and adjust the work time according to our needs.

The core time is usually from 9:00 am to 5:00 pm. At the beginning of a semester, we’re a little busy as we need to balance our work time between credit courses and our research. But we can seek advice and assistance from members and professors for all the troubles encountered in the research. I usually discuss my research with my supervisor Professor Tomioka, who would have discussions with students about their research plan and give great suggestions individually. Moreover, our laboratory is active in both domestic and international academic conference. Therefore, everyone in our group has plenty of chances to present their recent work at different places, which also offers a small local trip for us to experience various food and culture. We will hold a welcome party for new member who joins our group, organize a New Year’s Eve party at the end of year to reward our work and just enjoy some festivals such as beer garden together in Sapporo.

As a Chinese student, my life in this laboratory is busy but fulfilling. I have experienced countless failures in experiments, but as I overcome them one by one with the help of professors and members in our group, I have learned how to work as a researcher. All members are friendly to others and willing to offer help if someone is in trouble. There are lots of seasonal activities and events held by the university, where crowds of people gather at the camp and celebrate together. I always have a fun time there after work. Fitness room is also available, and I can get some exercise every week to keep my health. Sometimes foreign students will come to our laboratory and stay for several days or months for their internships, so we can communicate with students from other countries.

(2024/07/01)