Ge doped GaN and Al0.5Ga0.5N-based tunnel junctions on top of visible and UV light emitting diodes

Abstract

The use of tunnel junctions (TJs) is a potential solution in blue LEDs to poor p-contacts, replacing it by another n-contact. TJs are even more advantageous for UV emitting structures, which suffer from the considerably low injection efficiency in high Al concentration UV LEDs. In this work we report our work on Ge n-doped GaN and AlGaN TJs grown on top of blue and UV LEDs, respectively, by a hybrid growth. We have achieved state of the art mobility (67cm 2 /V.s) and resistivity (1.7x10 -4 Ω.cm) at a free electron concentration of 5.5x10 20 cm -3 in Ge-doped GaN. With an emission wavelength of 436nm, the GaN TJ slightly increased the optical power of the blue LED. The AlGaN TJs, on the other hand, improved the optical power of the UV LED (304nm) by at least a factor of 3, suggesting the enhancement of the hole injection efficiency by the use of TJs in UV emitting structures.

UVB LEDs Grown by Molecular Beam Epitaxy Using AlGaN Quantum Dots

“…Indeed, considering average values for the different efficiencies in our devices, i.e., with an IQE of 20%, an EE of 8% (estimated from the extraction cone at the sapphire/air interface) and an EQE of 0.05-0.1%, it is then possible to estimate the IE which is in the range of 3 to 6% only. Inefficient hole injection due to low hole concentration and mobility in high Al concentration Al x Ga 1−x N layers leads to electron leakage and overflow out of the active region and will require different layer designs such as tunnel junctions which have been shown as an attractive solution to improve the IE and avoid the use of an absorbing p-type GaN contact [46,47].…”

Effects of MOVPE Growth Conditions on GaN Layers Doped with Germanium

“…In the last few years there has been a renewed interest in highly doped n -GaN layers produced by metal-organic vapor-phase epitaxy (MOVPE). Such layers are very important for the optimization of the operative voltage of GaN-based electronic devices, especially those with tunnel junctions [ 1 ], as well as for controlling the layers’ refractive index thanks to the plasmonic effect [ 2 ]. For all these applications, it is desirable to reach higher doping levels than those achievable with silicon as a donor impurity.…”

Multi-microscopy nanoscale characterization of the doping profile in a hybrid Mg/Ge-doped tunnel junction

“…Even if Mg can be activated by annealing after the p-layer growth [20][21], it is at least partially re-passivated during the subsequent growth of the n-layer on top of the p-layer to fabricate the TJ. A new approach consists of growing the n + -side of the TJ by ammonia-based molecular-beam epitaxy (NH3-MBE) directly on an LED device synthesized by metal organic chemical vapor deposition (MOCVD) [7,22].…”

“…The aim of the present study is to correlate the chemical, structural and electrical properties of a Mg/Gedoped TJ grown on top of a InxGa1-xN/GaN-based LED. It has already been demonstrated that this architecture leads to an enhancement of the LED emission [22]. However, the in-depth understanding of the tunneling mechanisms requires an assessment of the distribution of dopants at the p/n interface, i.e.…”