Researcher Kang Tingting, State Key Laboratory of Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, made new progresses in the research of nitride photoconductors under very weak light with the support of the Chinese Academy of Sciences's Hundred Talents Project.
The researchers focused on experimental optics under extreme conditions (ie low light, low temperature, strong magnetic field) and designed a low-light photoconductive measurement system [shown below] with LED (light-emitting diode) The photoconductivity of InN is. Using the power density of light as an indicator, the incident light intensity ranged between 10-9-10-6W / cm2 (equivalent to the moon's intensity on the ground (~10-7W / cm2) only for full moon). International studies on photoconductivity use glare (0.1 - 100 W / cm2), which is 100,000 to 1 billion times the experimental light intensity. The researchers found that InN "persistent photoconductivity" completely disappeared in low light, and its behavior in bright light also met the three characteristics of light heating effect: (1) in line with the trend of thermal effects; (2) long relaxation Yu time; (3) increase with temperature drop. The results show that the InN "persistent photoconductivity" is derived from the light heating effect, indicating that InN has a strong electron-lattice effect; Physics Letters [Appl. Phys. Lett. 110, 042104 (2017)].
(a) Set up a weak light (low temperature LED) weak thermal radiation photoconductive measurement system. Use low temperature metal cover (~ 40K) to shield 300K black body heat radiation emitted by room temperature components. (b) Physical image of light heating effect
Photoconductivity measurement is an important method to study the optoelectronic properties of materials. It studies the change of electrical properties of objects under electromagnetic wave irradiation. Since W. Smith conducted research on the photoconductivity of selenium in 1873, photoconductivity has been an important research direction in the fields of optoelectronics and condensed matter physics and has directly led to the establishment and development of the application field of photodetector . However, due to the use of glare (mainly lasers), this area has been the subject of considerable controversy. Nitride, on the other hand, has been widely used in the fields of consumer electronics and white light as the third generation semiconductor. Akasaki Yo, Amano Koji and Nakamura Xiu won the 2014 Nobel Prize in Physics for their contributions to the field of nitrides. Indium nitride (InN), the only bandgap in III-nitride, located in the infrared (~ 0.7eV) material has important applications in applications such as nitride-based infrared detectors and full-spectrum high performance solar cells. Recently, in the field of InN, several research groups successively reported in the famous academic periodicals such as Phys. Rev. B, Appl. Phys. Lett., Sci. Rep. That there is a so-called "negative persistent photoconductive" photoconductivity, NPPC), ie: InN will slowly decline (so-called "negative" photoconductivity) after intense light (laser) irradiation.
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