Abstract
The effect of growth temperature and precursor flow on the doping level and surface morphology of Ge-doped GaN layers was researched. The results show that germanium is more readily incorporated at low temperature, high growth rate and high V/III ratio, thus revealing a similar behavior to what was previously observed for indium. V-pit formation can be blocked at high temperature but also at low V/III ratio, the latter of which however causing step bunching.
Highlights
The effect of growth temperature and precursor flow on germanium incorporation and surface morphology was studied in depth
It was found that the germanium incorporation depends on the growth conditions in a similar way to indium incorporation in InGaN layers, namely it increases at low temperature, high growth rate and high V/III ratio, whereas it does not increase linearly with the precursor flow but instead it saturates and it slowly decreases
Even though our study involved only GaN samples, with caution some conclusions can be taken for the other group III–nitride alloys
Summary
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]. Germanium has emerged as a better alternative to silicon as a donor dopant While it has a similar activation energy [5,6] and provides similar carrier mobility at every doping level [7], germanium has proved capable of attaining doping levels beyond 1020 cm−3 without negatively affecting surface morphology [3,8] nor introducing mechanical strain in the epitaxial structure [3,9].
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