Haojun Zhang and laser team are featured on Semiconductor Today
August 7, 2020
6 August 2020
CW operation of semi-polar GaN-on-sapphire laser
University of California Santa Barbara (UCSB) in the USA claims the first continuous-wave (CW) electrically driven semi-polar gallium nitride (GaN) blue laser diodes (LDs) at room temperature heteroepitaxially grown on 4-inch sapphire substrate [Haojun Zhang et al, ACS Photonics, vol7, p1662, 2020]. The researchers see their work as “a significant breakthrough in substantially reducing the cost of semi-polar laser diodes and expediting the development of future semi-polar GaN laser diodes and their applications”.
The team believes that topside flip-chip bonding to a high thermally conductive substrate such as silicon carbide could significantly improve laser diode performance and WPE under CW operation.
Study of the optical polarization of the emissions showed it to be almost 100% transverse electric (TE), as opposed to transverse magnetic (TM), at 1100mA injection. This was expected behavior.
Figure 1: (a) Image of 4-inch (20-21) GaN on sapphire substrate; (b) x-ray diffraction rocking curves of on-axis (20-21) plane with axis perpendicular and parallel to patterned stripes; bright-field cross-sectional transmission electron microscope images under two-beam conditions along (c) g =  and (d) g = [10-10] diffraction vectors with [11-20] zone axis.
Figure 2: (a) Laser diode structure; (b) scanning electron micrograph of 1800μmx8μm laser diode; (c) electroluminescence (EL) and far-field image of laser diodes above lasing threshold; (d) EL spectra with injection current density of 0.8x and 1.05x threshold; (e) light output power and voltage versus current of 1800μmx8μm laser diode under pulsed operation at room temperature.
Figure 3: (a) Light output power and voltage versus current density for 1500μmx8μm laser diode under CW operation and (b) WPE performance for pulsed and CW modes.