Solubility Limit of Ge Dopants in AlGaN: A Chemical and Microstructural Investigation Down to the Nanoscale

Attaining low-resistivity AlxGa1–xN layers is one keystone to improve the efficiency of light-emitting devices in ultraviolet spectral range. Here, we present a microstructural analysis AlxGa1–xN/Ge samples with 0 ≤ x 1, and nominal doping level range 1020 cm–3, together measurement Ge concentration its spatial distribution down nanometer scale. 0.2 do not any sign inhomogeneity. However, > 0.4 display μm-size crystallites at surface. segregation restricted surface: Ge-rich regions size tens nanometers are observed inside layers, generally associated Ga-rich around structural defects. With these local exceptions, matrix presents homogeneous composition which can be significantly lower than level. Precise measurements provide view solubility diagram as function Al mole fraction. The AlN extremely low. Between GaN, increases linearly Ga fraction ternary alloy, suggests that incorporation takes place by substitution atoms only. maximum percentage sites occupied saturates 1%. issues phenomena different length scales likely play role an n-type AlGaN dopant, even concentrations where DX centers expected manifest. Therefore, this information have direct impact on performance Ge-doped diodes, particularly for disinfection (≈260 nm), requires heavily doped alloys high