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FEBRUARY 2020        TAP TIMES       -11-           Making semiconductor diodes that emit
                                                                blue light has always been a challenge,
                                                                Yang said. The 2014 Nobel Prize for Phys-
                     Blue LED (from 10)                         ics was awarded for the breakthrough cre-
                                                                ation of efficient blue light-emitting diodes
        “Some people may say this is a limitation.              from gallium nitride.
        For me, this is a great opportunity,” said
        Yang, the S. K. and Angela Chan Distin-
        guished Chair in Energy in the College of               Different thinking
        Chemistry.                                              We need to think in different ways of using
                                                                this class of semiconductor,” Yang said.

        New physics                                             “We should not put halide perovskites
        “This is new physics: a new class of semi-              into the same application environment as
        conductors that can be readily reconfig-                a traditional covalent semiconductor, like
        ured, depending on what sort of environ-                silicon. We need to realize that this class
        ment you put them in. They could be a                   of material has intrinsic structural proper-
        really good sensor, maybe a really good                 ties that make it ready to reconfigure. We
        photoconductor, because they will be very               should utilize that.”
        sensitive in their response to light and

        Current semiconductors made of silicon
        or gallium nitride are very stable over a                 Feb. 4-6, SPIE Photonics West, San Francisco,
        range of temperatures, primarily because
        their crystal structures are held together                Feb. 4-6, APEX IPC, San Diego,
        by strong covalent bonds.
                                                                  Feb. 5-7, SEMICON Korea, Seoul, Korea, semicon-
        Held together by ionic bonds                              Feb. 10-13, Pan Pacific Microelectronics, Hawaii,
        Halide perovskite crystals are held to-         
        gether by weaker ionic bonds, like those
        in a salt crystal. This means they’re easier              Feb. 11-13, Medical Design and Manufacturing,
        to make — they can be evaporated out of                   Anaheim, Calif.,
        a simple solution — but also susceptible                  March 1-4, TestConX, Mesa, Arizona,
        to humidity, heat and other environmental       

        “This paper is not just about showing
        off that we made this blue LED,” said                                   ADVERTISERS
        Yang, who is a senior faculty scientist at
        Lawrence Berkeley National Laboratory
        (Berkeley Lab) and a UC Berkeley profes-                   Contech Solutions
        sor of materials science and engineering.                  E-Tec           
                                                                   HCD Corp.
        “We are also telling people that we re-                    Mirror Semiconductor
        ally need to pay attention to the structural               Nordson DAGE    
        evolution of perovskites during the de-                    Precision Contacts
        vice operation, any time you drive these                   TestConX        
                                                                   Test Tooling Solutions
        perovskites with an electrical current,                    Topline         
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