Self-compensation in heavily Ge doped AlGaN: A comparison to Si doping

Abstract

Self-compensation in Ge- and Si-doped Al0.3Ga0.7N has been investigated in terms of the formation of III vacancy and donor-vacancy complexes. Both Ge- and Si-doped AlGaN layers showed a compensation knee behavior with impurity compensation (low doping regime), compensation plateau (medium doping regime), and self-compensation (high doping regime). A maximum free carrier concentration of 4–5 × 1019 cm−3 was obtained by Ge doping, whereas Si doping resulted in only half of that value, ∼2 × 1019 cm−3. A DFT calculation with the grand canonical thermodynamics model was developed to support the hypothesis that the difference in self-compensation arises from the difference in the formation energies of the VIII-n•donor complexes relative to their onsite configurations. The model suggested that the VIII-2•donor and VIII-3•donor complexes were responsible for self-compensation for both Ge- and Si-doped AlGaN. However, a lower free carrier concentration in Si-doped samples was due to a high VIII-3•Si concentration, resulting from a lower energy of formation of VIII-3•Si.

Tracking of Point Defects in the Full Compositional Range of AlGaN via Photoluminescence Spectroscopy

“…[ 40–42 ] Ge was initially predicted to undergo a DX‐type transition; however, Bagheri et al determined that Ge transitioned to a deeper donor rather than a compensating acceptor state. [ 43 ] Based on this work, Ge showed potential for high carrier concentration with maximum achieved carrier concentration of 4–5 × 10 19 cm −3 in Al 0.3 Ga 0,7 N. [ 7,43 ] However, self‐compensation due to V III – n Ge complexes has been observed in AlGaN as well. [ 7 ] While the different charge states of V III ‐related complexes cannot be discerned from PL due to the broadness of the defect peaks, it has been found that the electrically neutral V III – 3•donor and acceptor‐type V III – 2•donor are mainly responsible for self‐compensation.…”

“…In addition, the onset of the knee depends also on the growth conditions, as dictated by the change in the defect formation energy with process supersaturation. [ 7 ] The RT PL spectra of V III – n Si complexes for various compositions of AlGaN are shown in Figure and the emission energies are summarized in Figure .…”

Towards Efficient Electrically-Driven Deep UVC Lasing: Challenges and Opportunities

“…Some data points in the range of 10 18 < [Si] < 10 19 cm −3 exhibit considerable deviations from the grey line in Figure 3 . This fact may be attributed to a reduction of the electrical conductivity by parasitic impurities, mainly by carbon, being a compensating acceptor in MOVPE [ 61 ], and mainly by oxygen in the case of MBE [ 62 ].…”

“…Recently, the advantages of using Ge instead of Si have been demonstrated for n-type doping of Al 0.3 Ga 0.7 N [ 61 ]. Ge donors were capable of producing three-times higher maximum electron concentration than Si.…”

Role of Metallic Adlayer in Limiting Ge Incorporation into GaN

“…This element can be used in a much wider doping spectrum without degrading surface morphology [ 7 ]. It was also reported that Ge doping leads to lower compensation than Si, resulting in higher carrier concentrations at high doping levels [ 13 , 14 ]. Ge doping was also used to significantly lower the refractive index of GaN [ 15 ].…”