Seminarium Fizyki Ciała Stałego

Gallium nitride-based tunnel junctions are a key element enabling the design and fabrication of novel optoelectronic devices such as vertically integrated stacks of laser diodes or multicolor light-emitting diodes1. However, the wide energy bandgap of GaN results in a high tunneling barrier and therefore high series resistance of tunnel junctions. In the literature, two different methods have been proposed to increase the electric field in the junction, thereby increasing the tunnel current: introducing polarization fields into the structure from an undoped (In,Ga)N layer2, and heavy doping of GaN p-n junction3. However, these two methods have been considered separately so far.

Within this seminar, I will present an innovative tunnel junction structure, produced by plasma-assisted molecular beam epitaxy (PAMBE), in which the (In,Ga)N layer is in addition doped with magnesium in one half and silicon in the other4. The influence of tunnel junction structural parameters, such as dopants level, indium content and width of (In,Ga)N layer, on their electrical properties and crystalline quality is analyzed. As a result, a remarkably low voltage drop on the tunnel junction is achieved (0.27 V at 1000 A/cm2), preserving the atomically smooth surface morphology. In addition, a tunneling model based on Kane's theory has been developed, quantitatively consistent with experimental results. This model considers the electric field generated in the junction as a result of both doping and polarization fields, and employs an effective hole mass from the crystal field split-off band (CH), which for GaN is 0.14 m0.

Research into tunnel junctions has led to the invention of a bidirectional light-emitting diode (BD LED) structure that can operate directly under the alternating current (AC)5. This is an innovative structure with two tunnel junctions surrounding the active region, which allow current flow and light emission in both directions of supplied power. In addition, the influence of polarization fields on the operation of this diode is analyzed and the opportunity to increase optical power through their vertical integration is presented.


Acknowledgments: This work was supported by National Science Center Poland within grant No. 2023/49/N/ST7/03786.

References:

1 Siekacz, M. et al. Vertical Integration of Nitride Laser Diodes and Light Emitting Diodes by Tunnel Junctions. Electronics 9, doi:10.3390/electronics9091481 (2020).
2 Krishnamoorthy, S., Akyol, F., Park, P. S. & Rajan, S. Low resistance GaN/InGaN/GaN tunnel junctions. Applied Physics Letters 102, 113503, doi:10.1063/1.4796041 (2013).
3 Young, E. C. et al. Hybrid tunnel junction contacts to III–nitride light-emitting diodes. Applied Physics Express 9, 022102, doi:10.7567/APEX.9.022102 (2016).
4 Żak, M. et al. Tunnel Junctions with a Doped (In,Ga)N Quantum Well for Vertical Integration of III-Nitride Optoelectronic Devices. Physical Review Applied 15, 024046, doi:10.1103/PhysRevApplied.15.024046 (2021).
5 Żak, M. et al. Bidirectional light-emitting diode as a visible light source driven by alternating current. Nature Communications 14, 7562, doi:10.1038/s41467-023-43335-7 (2023).