Abstract
Dislocations in undoped GaN move in response to the in-plane tensile stress present during film growth. Dislocation movement during growth relieves tensile stress, produces arrays of a-type dislocations and reduces the overall dislocation density, with preferential reduction of (a+c)-type dislocations. However, Si-doping limits dislocation movement, limiting the relief of the tensile stress that develops during growth and limiting dislocation reduction, probably due to the formation of Si impurity atmospheres at dislocations. Consequently, Si-doped films are under relatively greater tensile stress compared to undoped GaN films grown under similar conditions. Alternative dopants could be chosen to reduce tensile stress development, such as Ge.
| Original language | English |
|---|---|
| Article number | 073509 |
| Number of pages | 7 |
| Journal | Journal of Applied Physics |
| Volume | 109 |
| Issue number | 7 |
| DOIs | |
| Publication status | Published - 1 Apr 2011 |
Funding
The authors acknowledge support from the Engineering and Physical Sciences Research Council. M. A. M. would like to acknowledge support from the Oppenheimer Trust and Jesus College, Cambridge through personal fellowships. R.A.O. would also like to acknowledge support from the Royal Society through a University Research Fellowship. FIG. 1. Plot of the total dislocation density detected at the film surface as a function of film thickness for (a) a series of undoped GaN films (filled symbols, lower trace on the plot) and (b) a series of GaN films doped with Si to a concentration of 1 × 10 19 cm −2 , apart from the first 200 nm of the film, which is undoped (open symbols, upper trace on the plot). FIG. 2. Plot of the full widths at half maximum of the X-ray diffraction ω-scans taken from (a) the 20 2 ¯ 1 reflection and (b) the 0002 reflection, for undoped GaN films (filled symbols, lower trace on the plots) and for GaN films doped with Si to a concentration of 1 × 10 19 cm −2 , apart from the first 200 nm of the film, which is undoped (open symbols, upper trace on the plots). FIG. 3. Plot of the percentage of all dislocations that are a -type as a function of film thickness for undoped GaN films (filled symbols, upper trace on the plot) and for GaN films doped with Si to a concentration of 1 × 10 19 cm −2 , apart from the first 200 nm of the film, which is undoped (open symbols, lower trace on the plot). FIG. 4. (a) Plan view AFM topography image of a 1000 nm thick GaN film (Z-scale = 8 nm) and (b) an RDF plot of dislocation surface positions from that film (in which black symbols indicate data points and gray symbols indicate 99% confidence intervals); (c) Plan view AFM topography image of a 1000 nm thick GaN film doped with Si to a concentration of 1 × 10 19 cm −2 , apart from the first 200 nm of the film, which is undoped (Z-scale = 13 nm), and (d) an RDF plot of dislocation surface positions from that film (in which black symbols indicate data points and gray symbols indicate 99% confidence intervals). FIG. 5. Plot of the “clustering index” as a function of film thickness for nominally undoped GaN films (filled symbols, upper trace on the plot) and for GaN films doped with Si to a concentration of 1 × 10 19 cm −2 , apart from the first 200 nm of the film, which is undoped (open symbols, lower trace on the plot). For these samples, corrected densities greater than approximately 1.3 indicate significant clustering. Lines are merely a guide to the eye. FIG. 6. Plots of the wafer curvature (solid lines) and susceptor temperature (dashed lines) as a function of growth time for (a) a 1000 nm high dislocation density nominally undoped GaN film and (b) a 1000 nm high dislocation density GaN film doped with Si to a concentration of 1 × 10 19 cm −2 , apart from the first 200 nm of the film, which is undoped. (c) A comparison of the wafer curvature during growth of the final 800 nm of both films, in which data from the undoped film are shown as a solid line and data from the doped film are shown as a dashed line.
Keywords
- tensile stress
- dislocation movement
- Si-doped films
- GaN films