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HL: Fachverband Halbleiterphysik

HL 52: Nitrides: Devices

HL 52.3: Vortrag

Freitag, 22. März 2024, 10:00–10:15, EW 015

Impact of overgrowth conditions on characteristics of tunnel-junction LEDs — •Christoph Berger, Armin Dadgar, and André Strittmatter — Otto-von-Guericke-Universität Magdeburg

The implementation of tunnel-junctions (TJs) on the p-side of blue light emitting diodes (LEDs) offers an exciting way to realize transparent, highly conductive electrodes for enhanced hole injection, better current spreading and higher efficiency. We realized TJ-LEDs by growth of a 100 nm thick GaN:Ge layer with an electron concentration of 1x10²⁰ cm⁻³ on top of the GaN:Mg layer in a continuous growth process by MOVPE. No in-situ or ex-situ activation steps were carried out and even 1 mm² LEDs show homogeneous light emission with improved output power. We propose that the activation of the p-GaN occurs during overgrowth with the GaN:Ge layer. Although n-doped GaN is known to block hydrogen diffusion, we assume an out-diffusion of H₂ promoted by V-pits that are formed during GaN:Ge growth in nitrogen ambient. Growing an additional GaN:Si layer in H₂-ambient on top of the TJ-LED for surface smoothening detoriates the optical and electrical characteristics of the device, suggesting repassivation of p-GaN by H₂ diffusion through the GaN:Ge layer. We will show results of different overgrowth schemes to elucidate the activation process for further improvement of device characteristics especially with regard to cascaded LEDs

Keywords: GaN; tunnel junction; LED; MOVPE; doping