Role of Metallic Adlayer in Limiting Ge Incorporation into GaN

Atomically thin metal adlayers are used as surfactants in semiconductor crystal growth. The role of the adlayer in the incorporation of dopants in GaN is completely unexplored, probably because n-type doping of GaN with Si is relatively straightforward and can be scaled up with available Si atomic flux in a wide range of dopant concentrations. However, a surprisingly different behavior of the Ge dopant is observed, and the presence of atomically thin gallium or an indium layer dramatically affects Ge incorporation, hindering the fabrication of GaN:Ge structures with abrupt doping profiles. Here, we show an experimental study presenting a striking improvement in sharpness of the Ge doping profile obtained for indium as compared to the gallium surfactant layer during GaN-plasma-assisted molecular beam epitaxy. We show that the atomically thin indium surfactant layer promotes the incorporation of Ge in contrast to the gallium surfactant layer, which promotes segregation of Ge to the surface and Ge crystallite formation. Understanding the role of the surfactant is essential to control GaN doping and to obtain extremely high n-type doped III-nitride layers using Ge, because doping levels >10(20) cm(-3) are not easily available with Si.

Automated summary

Atomically thin metal adlayers are used as surfactants in semiconductor crystal growth, with the role of the adlayer in dopant incorporation in GaN being unexplored. Experimental study shows that the presence of atomically thin gallium or indium layers dramatically affects Ge incorporation in GaN, with indium surfactant layer promoting Ge incorporation while gallium surfactant layer promotes segregation of Ge to the surface. Understanding the role of surfactants is crucial for controlling GaN doping and achieving high n-type doping levels using Ge.