Vacancy-engineering-induced dislocation inclination in III-nitrides on Si substrates

The incorporation of point defects into semiconductors could substantially tailor their optical and electrical properties as well as the spin-based quantum properties. In terms of structural properties, however, efforts have seldom been devoted to the relevant aspects. Herein, we propose point defects engineering by intentionally introduced vacancies to improve the structural properties. GaN-on-Si are selected as a paradigm to demonstrate the applicability of this approach. By tuning the growth stoichiometry, nonequilibrium Ga vacancies are intentionally introduced and absorbed by dislocation cores, which leads to dislocation inclination and annihilation in GaN. In addition, this dislocation inclination can proceed without relaxing the compressive lattice stress. These together enable high quality GaN thick layers on Si substrates with dislocation density of $1.6\times {10}^8\mathrm{c}{\mathrm{m}}^{-2}$ and a record electron mobility of $1090\mathrm{c}{\mathrm{m}}^2/\mathrm{V}\mathrm{s}$ at a carrier density of $1.3\times {10}^{16}\mathrm{c}{\mathrm{m}}^{-3}$. With these advances, a quasivertical GaN Schottky barrier diode with the lowest specific on-resistance of $0.95\mathrm{m}\mathrm{\Omega }/\mathrm{c}{\mathrm{m}}^2$ and highest on/off ratio of ${10}^{10}$ on Si substrates is demonstrated. These results demonstrate the promise of point defect engineering as a strategy to improve the structural properties and pave the way for high-performance III-nitride based electronic and optoelectronic devices on Si platforms.

Figure 1

(a) Schematic diagram for the growth of vacancy-engineered sample. The Ga vacancies are introduced by tuning the flow rate of TMGa and $\mathrm{N}{\mathrm{H}}_3$ (V/III molar ratio). (b) $\mathrm{S}$ parameters as a function of positron energy for GaN layer with and without performing vacancy engineering. The increased $\mathrm{S}$ parameter indicates that more Ga vacancies could be incorporated by employing the vacancy engineering.

Figure 2

Cross-section $g=\left(11\overline{2}0\right)$ weak-beam dark-field TEM image of the sample without (a) and with (b) performing vacancy engineering. In the sample without vacancy engineering, most dislocations originating from the AlGaN/GaN interface (marked with white dash line) incline with small angles and thus propagate into the upper GaN layer. In contrast, most dislocations incline with large angles or even incline horizontally in the vacancy-engineered sample. (c) Asymmetric (102) scans of rocking curve for the two GaN samples. The FWHM is 715 and 379 arcsec for the sample without and with performing vacancy engineering, respectively.

Figure 3

Stress analysis for the two samples. (a) Raman spectra of GaN film with and without performing vacancy engineering. The residual stress in the conventional sample and vacancy-engineered sample is tensile and compressive stress, respectively. Cross-sectional Raman spectra for the GaN layer without (b) and with (c) performing vacancy engineering. A gradual redshift of the $E_2$ (high) peak position and almost no shift of the $E_2$ (high) peak position for the two samples can be observed. No shift of the $E_2$ (high) peak position indicates the vacancy engineering can suppress the stress relaxation and thus maintain the compressive stress very well.

Figure 4

Mechanism of Ga vacancies induced dislocations inclination. The atomic plane painted with purple is the extra $\left(11\overline{2}0\right)$ half plane. The red line shows the inclined threading dislocation. The nonequilibrium Ga vacancies are absorbed at the jogs in the dislocation core intersected with the growth surface, and consequently promote the dislocation inclination.

Figure 5

Demonstration of a quasivertical GaN-based SBD on Si. (a) Schematic architecture of the quasivertical GaN SBD grown on Si substrates. (b) AFM image of the surface of the GaN film, showing a step-flow surface morphology with a rms of 0.15 nm. (c) Panchromatic CL image of the GaN film. The density of the dark spots, representing the dislocation density in the GaN film grown on Si, is about $1.6\times {10}^8\mathrm{c}{\mathrm{m}}^{-2}$. (d) Plan-view TEM image of the GaN film. The estimated dislocation density is about $1.8\times {10}^8\mathrm{c}{\mathrm{m}}^{-2}$, which is well consistent with the CL results. (e) Linear scale forward I-V characteristics (black) and corresponding specific on-resistance (blue). The SBD exhibits a high forward current density of $1.9\mathrm{kA}/\mathrm{c}{\mathrm{m}}^2$ at 3 V and a low specific on-resistance of $0.95\mathrm{m}\mathrm{\Omega }/\mathrm{c}{\mathrm{m}}^2$. (f) Log scale I-V characteristics, showing a record current on/off ratio of ${10}^{10}$ for the GaN SBD on Si substrate.