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Controlling GaN-on-silicon(001) growth with insitu monitoring

Laytec has reported EpiCurve TT results obtained during the growth of gallium nitride HEMTs on Si(001) substrates
The growth of GaN on Si(111), especially for LEDs, is quite well known and relatively controllable.

Cooldown-assisted layer cracking as a result of high tensile stress can be prevented and crystal quality can be enhanced by sophisticated interlayers. Many institutions are using LayTec‘s EpiCurve TT tool with advanced curvature resolution to grow high quality GaN devices on large scale (111) silicon substrates.

Now, this experience is being transferred to growth on Si(001) and Si(110) substrates. This is because GaN based power electronics can be easily integrated with standard silicon electronics (CMOS). What's more, like Si(111), these substrates are also available in large sizes of up to 300 mm.

In October 2012, Jonas Hennig of Otto-von-Guericke Universität Magdeburg in Germany reported results on high performance GaN HEMT structures grown on Si(001). The structures incorporated highly optimised interlayers to control stress and defect density.

The results were presented at the International Workshop on Nitride Semiconductors in Japan.

According to Hennig, in-situ growth monitoring by Epi-Curve TT is a great help for their strain engineering.

The well pronounced  Fabry-Perot oscillations at 633 nm (red) and 950 nm (blue) in correlation with the smooth development of the curvature show the high quality of the GaN. What's more, during the growth of interlayers, when the temperature is being reduced, an abrubt increase in curvature can be observed as shown in Figure 1 below.

Figure 1: In-situ measurements of temperature (red) and curvature (black)by EpiCurve TT during GaN on Si(001) growth.

The three combined reflectance signals help to determine the growth rates and allow adjustment of the growth parameters. In addition, the 405 nm reflectance (the black line in Figure 2 below), provides information on the structural interface quality.

Figure 2: In-situ reflectance measurements by EpiCurve TT at three wavelengths:

blue – 950 nm, red – 633 nm, black - 405nm

The work at Otto-von-Guericke University and other institution which use LayTec‘s in-situ tools for silicon applications shows that the quality of GaN-on-silicon can be significantly improved by advanced curvature monitoring in combination with multiple wavelength reflectance.

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