Incorporation of Er into GaN by in-situ Doping During Halide Vapor Phase Epitaxy
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Er surface segregation during growth has been observed in these samples. All in-situ Er-doped GaN samples present a sharp bandedge luminescence band. No yellow luminescence (YL) band is detected in any of the GaN:Er samples. The Er-doped GaN emits sharp 1.54 jtm luminescence at both low and room temperatures. Higher Ga/Er source temperatures leads to stronger and sharper 1.54 jtm Er ion luminescence. EXPERIMENTS AND RESULTS All GaN:Er samples used in this study were grown on (0001) sapphire substrates in a horizontal atmospheric pressure HVPE system. The details of the reactor and growth technique have been previously reported[16]. NH 3 was used as the nitrogen source and its mole fraction was held constant at 0.11. GaCI and ErC13, which were produced from the reaction between metallic Ga (7N) and Er (3N) in the Ga/Er boat and the introduced HCI, were used as Ga/Er source to grow
GaN:Er films. The input ratio of NH 3-to-HCI was kept at 30. N 2 was used as a carrier gas. The Ga/Er boat was set at a temperature either 850 or 880 0C, while the substrate temperature remained at 1030 0 C. Formation of a miscible Ga-Er liquid requires an Er weight percentage less than 23% at 850'C and 27% at 880'C. In this study, the weight ratio of Er-to-Ga was set to 1:5. No other intentional dopants, besides Er, were used. All GaN:Er films are grown along the (0001) direction with a surface morphology that is 1E20 dominated by large hexagonal features, which is typically observed for HVPE-grown GaN films[17]. S(The surface is, however, much rougher for high Ercontent GaN films than the unintentionally[18] or Cdoped[19] GaN films, or films grown with H 2 addition into the growth ambient[20,21]. Some cracks, many of them are very regular, can be seen in most samples due to thermal expansion mismatch during cooling. A few small pits appear along the particularly at the points of intersection of the
14-
1E18
E
E
C C 1I)E17 (b)
S
11cracks,
,W 1E15 1E141_source 0.0
0.5
1.0 Depth (gm)
1.5
2.0
Fig. I Typical SIMS depth profile of Er
concentration of GaN:Er films grown by HVPE with the metal source temperature at 880 0C (a) and 850'C (b). The Er concentration of the sample A (grown with the metal source 3 temperature of 880'C) is 2 x 10i1cm" (a), and that of the sample B (grown with the metal 3 source temperature of 850°C) is 1 x 1016 cm" (b). This result implicates that the higher Ga/Er boat temperature with its higher growth rate leads to a higher concentration of Er ions in the GaN film. The Er surface segregation during the GaN:Er growth can also be seen from this figure.
cracks. The films exhibit n-type conductivity with the typical carrier concentration of -1019 cm-3 at room temperature. The samples grown at a Ga/Er temperature of 850 0C have a growth rate of 20 jim/hr and those grown with an 880 0 C metal source have a growth rate of 40 jim/hr. The growth rate is less than undoped GaN conditions[18]. ranges between
-100 jtm/hr, obtained for nominally films grown under the similar The thickness of samples studied 20-40 j
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