Synthesis of Nitrogen-Rich GaNAs Semiconductor Alloys and Arsenic-Doped GaN by Metalorganic Chemical Vapor Deposition
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s atomic %] [As atomic %] + [N atomic %]
;
s=
[Ga atomic %] [As atomic %] + [N atomic %]
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Secondary ion mass spectroscopy (SIMS) analysis was also performed for quantification purposes, with the CsM+ molecular ion technique used for GaNAs alloys,6 and an arsenic implant standard employed to calibrate arsenic doping. Transmission electron microscopy (TEM) and x-ray diffraction (XRD) measurements were performed to evaluate the structural properties of these materials. III. RESULTS A. Effects of Growth Temperature on Arsenic Incorporation The general trend observed in all experiments is that an increase in growth temperature leads to a decrease in arsenic incorporation. Table I summarizes our observations for samples grown with an arsine flow of 4 sccm. These films were deposited on GaN pseudo-substrates, except for the 1030 ˚C sample which was grown using the two-step method. At 950 and 1030 ˚C the arsenic content is below the EPMA detection level so SIMS analysis was used for quantification. Table I. Arsenic incorporation dependence on growth temperature. Temperature (˚C)
Composition (%)
Measurement
Stoichiometry (s)
700
3.2 ± 0.3
EPMA
0.98 ± 0.02
800
0.19 ± 0.02
EPMA
0.96 ± 0.02
900
0.10 ± 0.04
EPMA
0.98 ± 0.02
950
0.02
SIMS
0.99 ± 0.01
1030
2 x 1016 cm-3
SIMS
0.97 ± 0.02
B. Effects of Substrate Material on Phase Separation The phase distribution of GaNAs films grown at 700 ˚C exhibits a strong dependence on the choice of substrate. Phase segregation was observed in some samples, Table II, with multi-faceted GaAs particles (average size ≈ 10–30 µm) precipitating on top of specular GaNAs films. For cases were more than one phase is present, EPMA measurements were conducted on all visually distinct features. The influence of substrate in the present work is consistent with the well-documented composition pulling phenomenon7 (e. g., the trend for samples grown with 4 sccm of arsine). C. High Temperature Growth of Arsenic-Doped Gallium Nitride Previously we demonstrated that arsenic doping significantly improves the electronic properties of GaN epitaxial layers.8 The present work confirms our original findings, and provides additional data on the chemical and structural properties of these materials. At a growth temperature of 1030 ˚C, the arsenic doping level increases from 2 x 1016 to 2 x 1017 cm-3 in Table II. Phase distribution dependence on substrate and arsine flow. AsH3 flow → Substrate↓
4 sccm
40 sccm
400 sccm
GaN
GaNAs
GaNAs + GaAs
GaAs
Al2O3
GaNAs + GaAs
GaAs
GaAs
GaAs
GaAs
GaAs
NA
2 Downloaded from https://www.cambridge.org/core. IP address: 109.94.221.100, on 23 Mar 2019 at 00:06:01, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/S1092578300002623
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