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Gallium Nitride - Hydride Vapor Phase Epitaxy

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Fig. 1
Fig. 1:  2” GaN crystal grown on a for self-separation optimized FACELO template. It is 2.5 mm thick with only a few Vpits and a smooth and specular surface.

Since 2011 NaMLab is belonging to a elite group of bulk-GaN growers. It is cooperating onsite with Freiberger Compound Materials (FCM) in Freiberg and owns a state of the art vertical HVPE reactor. Main focus of the development lies on the growth of thick semi-insulating as well as n-type doped GaN-crystals (Fig. 1).
The vertical HVPE reactor has four different possibilities for introducing dopants. Dopants are used for adjusting the electrical and optical properties of the GaN-crystals. The doping possibilities have been investigated thoroughly in the last two years.
Solid state doping is the most straightforward and cost efficient way to dope GaN. With this method the dopant is introduced as a solid to the reactor and an in-situ chemical reaction is utilized to form a gaseous chemical compound which is added to the existing gas flux. The chemical compound is transported to the growth surface and incorporated into the GaN. Germanium has been used to achieve n-type doping in GaN. A chlorination reaction formed a mixture of GeHCl3/GeCl4. These gaseous compounds are incorporated during crystal growth. By this GaN:Ge crystals were grown utilizing the solid-state doping line. SIMS and room-temperature Hall measurements confirm the success of the n-type doping with Ge.

Fig. 2
Fig. 2: SEM cross-section micrograph of pulsed GaN:Ge doping layers. The multilayer structure results from a spatially localized supply of the dopant coupled with the rotation of the GaN crystal during growth.


A closer investigation of the dopant incorporation reveals an improved lateral incorporation of the dopant, however due to substrate rotation the doping concentration oscillates perpendicular to the growth direction. The varying doping concentration can even be investigated by SEM. Fig. 2 shows the SEM micrograph of a pulsed Ge doping. In contrast to continuous doping, a pulsed doping can be used to investigate the growth surface after the crystal growth. Dark lines with high Ge concentration are visible. The enlargement makes dark lines visible resulting from the pulsed Ge-doping. The line structure stems from a strongly localized dopant supply inside the reactor while the growing crystal rotates. The fine structure of a Ge doping pulse can be exploited to extract information about the growth velocity of specific GaN facets during growth and how it reacts to changes in growth parameters. Fig. 3 shows the growth velocity of the (0001) facet as a function of the crystal growth temperature.

Fig. 3
Fig. 3: Growth velocity of the (0001) GaN facet vg(0001) as a function of the growth temperature T. Such ex-situ investigations of the influence of growth parameters were made possible by the GaN:Ge doping via solid state doping line.




Other doping methods such as the metal organic precursor doping for reaching semi-insulating GaN via ferrocene (Cp2Fe) was established and investigated. GaN:Fe was successfully grown with iron concentrations from 5x1015 to 8x1017 cm-3. Room temperature Hall measurements corroborated the observed iron incorporation and showed a specific resistance of the GaN:Fe layers up to 1x103 Ωcm.



Contact: Dr. Martin Krupinski


NaMLab gGmbH
Nöthnitzer Str. 64 a
01187 Dresden

Tel. +49.351.21.24.990-00
Fax. +49.351.475.83.900




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