The investigation of stress in freestanding GaN crystals grown from Si substrates by HVPE

Moonsang Lee,Mino Yang,Dmitry Mikulik,Sungsoo Park

doi:10.1038/s41598-017-08905-y

Abstract

We investigate the stress evolution of 400 µm-thick freestanding GaN crystals grown from Si substrates by hydride vapour phase epitaxy (HVPE) and the in situ removal of Si substrates. The stress generated in growing GaN can be tuned by varying the thickness of the MOCVD AlGaN/AlN buffer layers. Micro Raman analysis shows the presence of slight tensile stress in the freestanding GaN crystals and no stress accumulation in HVPE GaN layers during the growth. Additionally, it is demonstrated that the residual tensile stress in HVPE GaN is caused only by elastic stress arising from the crystal quality difference between Ga- and N-face GaN. TEM analysis revealed that the dislocations in freestanding GaN crystals have high inclination angles that are attributed to the stress relaxation of the crystals. We believe that the understanding and characterization on the structural properties of the freestanding GaN crystals will help us to use these crystals for high-performance opto-electronic devices.

Highlights

Gallium nitride (GaN) is one of the most promising materials for optoelectronic devices such as laser diodes, ultra violet detectors, light-emitting diodes (LEDs), and power electronics[1,2,3]
The full width at half maximum (FWHM) for the (0002) X-ray rocking curve of the freestanding GaN was evaluated as 62 arcsec. (See Fig. S4) This value is comparable to or even better than those in GaN layers grown on other foreign substrates as reported elsewhere[4, 18]
We investigate the stress evolution of 400-μm-thick freestanding GaN crystals grown on Si by hydride vapour phase epitaxy (HVPE)

Summary

Results and Discussion

Note that the value of bowing in the MOCVD buffer layer/Si templates decreases with increasing MOCVD buffer layer thickness, implying the increase in the compressive stress in MOCVD buffer layers[13]. This implies that the presence of the MOCVD buffer layers successfully contributes to the strain compensation for growing HVPE GaN layers[13, 15]. We believe that this remarkable strain relaxation prevent the accumulation of tensile stress in the freestanding GaN during growth, enabling the growth of the freestanding GaN crystals from Si substrates

Conclusions

Author Contributions

Additional Information