GaN Growth by Remote Plasma MOCVD: Chemistry and Kinetics by Real Time Ellipsometry
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d from https://www.cambridge.org/core. IP address: 81.22.46.145, on 07 Mar 2019 at 07:06:06, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/S1092578300002416
used to produce H-atoms for the substrates cleaning, and N-atoms for the nitridation process and GaN growth. The H2 remote plasma cleaning was operated at P = 1 Torr, r.f. power = 60 Watt and at a surface temperature of 250°C and 350°C for GaAs (001) and α-Al2O3 (0001), respectively. The subsequent nitridation by N2-H2 (3% in H2) plasmas was operated at a pressure of 0.2 Torr, a r.f. power of 200 Watt and at a temperature of 250°C and 800°C for GaAs and α-Al2O3, respectively. GaN layers were grown at 600°C by trymethylgallium and N2/H2 (=1000/3 sccm) plasma at a pressure of 1 Torr and a r.f. power of 200 W. Single wavelength ellipsometry (SWE) was used, in terms of the ellipsometric angles Ψ and ∆ [6], to monitor in real time the surface kinetics, and, at the growth end, ellipsometric spectra (SE) of the pseudodielectric function, = + i , were acquired in the energy range 1.5 - 5.5 eV. In order to determine the chemical and optical properties of surfaces, ellipsometric data were modeled by optical models based on the Bruggeman effective-medium approximation (BEMA) [6] and references for the used dielectric functions are given in ref. [7]. Optical emission spectroscopy (OES) was used to control the N-atom density interacting with the growth surface. Ex situ atomic force microscopy (AFM) and X-ray diffraction (XRD) measurements were also performed to validate the ellipsometric approach. RESULTS AND DISCUSSION Figure 1 shows typical SWE real time (Ψ,∆) trajectories recorded at 3 eV during GaN growth on both α-Al2O3 (0001) and GaAs (001) substrates previously nitrided. An easily provided information is the GaN layer thickness which is controlled in real time. 400
400
nucleation
(a) 3eV
64 A
300
300
220
Chemical Interface
(b) 3 eV
GaN+2%Ga
480
2D-growth
∆° 200
∆° 200
300
2D-growth
430 530
830
100
end GaN+4%Ga
Ga N nucle us 2 50A
4
8 Ψ°
12
surfa ce roughness GaN
A l2 O 3
nucleation
16
A l2 O 3
coalescence
2D -grow th
start
840 1040
start
0 0
100 0 010
G aN clu ste r
end
20
voids
280A
Ψ°
30
40
surfa ce roughness
80% GaN 320A 2 1 % G a A s G aA s 1 8 % vo id s chem ical interface
GaN
Ga As
2D -grow th
FIGURE 1. Time evolution of the optical response in the (Ψ,∆) space at 3 eV during GaN growth on (a) α-Al2O3 and (b) GaAs. Points are for experimental data; full line is for the best-fit model which is, for GaN on α-Al2O3, nucleation followed by 2D-homogeneous growth and, for GaN on GaAs, chemical interface appearance followed by 2D-homogeneous growth. Simulated trajectories by different models (see text) are also reported for comparison.
Downloaded from https://www.cambridge.org/core. IP address: 81.22.46.145, on 07 Mar 2019 at 07:06:06, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10
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