Properties of GaN Films Grown by Atomic Layer Deposition Using Low-temperature III-nitride Interlayers J. R. Gong

1. Properties of GaN Films Grown by Atomic Layer Deposition Using Low-temperature III-nitride Interlayers J. R. Gong Department of Materials Science and Engineering Feng Chia University June 4, 2004

2. Co-workers C. L. Wang B. H. Shih Y. L. Tsai I. H. Chien W. T. Liao S. W. Lin

3. OUTLINE  Applications of III-nitrides • Fundamental aspects of ALD • LT-III-nitride interlayers — LT-GaN interlayer — LT-AlN interlayer — Ternary LT-AlGaN interlayer •  Conclusions

4. Elemental and compound semiconductors Column IV: Si, Ge, SiGe, SiC Column III and V: GaAs, InP, InAs, InSb, GaN and alloys Column II and VI: ZnSe, CdS, HgTe and alloys

5. Semiconductor bandgaps UV-wide bandgap (GaN, ZnSe) IR-narrow bandgap (InSb, HgTe) Direct (mostly III-V): light emission possible LEDs, Lasers Indirect (mostly Si): light emission forbidden  transistors, ICs

6. UV region Bandgap engineering

7. Research and development history of GaN

8. Advantages of III-nitrides  Direct band gap  The adjustability of band gap from 1.9eV (InN) to 6.2eV (AlN)  Good radiation hardness  High temperature resistance

9. Applications of III-nitride devices  HBLEDs — traffic signal — full-color outdoor display — back light for LCD  LDs — DVDs  High Power Electronics

10. Markets for nitride-based LEDs

11. LED traffic signal Reacting speed of LEDs is 20 times faster than traditional light bulbs.

12. Outdoor full-color LED display

13. LCD backlight

14. LED car indicators

15. LED general lighting

17. LED Chip substrate

18. Atomic Layer Deposition

19. Photographs of the home-made ALD growth system

20. A schematic diagram of the ALD system for the growth of III-nitride films Hydrogen Purifier Susceptor TMG TMA R.F. Coil H 2 Quartz NH 3 N 2 Exhaust Three-way Mass Flow Valve Regulator Valve Controller

21. A schematic diagram of the rotating susceptor for ALD process

22. Fundamental aspect of atomic layer deposition (ALD) (A) (B) AX AX AB(sub.) AB(sub.) (C) (D) BY AB (monolayer) AB(sub.) AB(sub.) • An ideal ALE growth cycle produces a monolayer AB compound.

23. Influence of low temperature GaN intermediate layers on the properties of GaN films

24.  HT: 1000 ℃ 150, 380, 600 nm A schematic structure of HT-GaN films without LT-GaN interlayer

25. (a) (b) (c) SEM micrographs of the surface morphologies of HT-GaN films grown on (0001) sapphire substrates 150 nm 380 nm 600 nm

26.  HT: 1000 ℃  LT: 500 ℃ (a) (b) (c) (d) Schematics of HT-GaN films inserted with LT-GaN interlayers

27. (a) (b) (c) (d) SEM surface morphologies of HT-GaN films inserted with a LT-GaN interlayer 7 nm 0 nm 20 nm 70 nm

28.  The arrangement of Ga adatoms is merited by the suppression of surface kinetics at low growth temperatures, which is believed to stop the extension of mosaic structure from the underlying 150 nm-thick HT-GaN film during the growth of LT-GaN interlayer. A LT-GaN interlayer thickness deviated away from its optimised value was observed to deteriorate the quality of the subsequently grown HT-GaN film.  The role of LT-GaN interlayer on the growth of HT-GaN film

29. RT PL spectra of HT-GaN films inserted with different LT-GaN interlayer thicknesses (The inset shows the effect of interlayer thickness on the PL emission energy)

30. (0002) DCXRD curve of a HT-GaN film inserted with a 20-nm-thick LT-GaN interlayer

31. Cross-sectional TEM image of a HT-GaN film inserted with a 20-nm-thick LT-GaN interlayer

32. A schematic structure of GaN films having various LT-GaN interlayer thicknesses HT-GaN 0.9 m LT-GaN 25Å<d<300Å HT-GaN 0.6 m AlN buffer sapphire

33. RT PL spectra of GaN films inserted with LT-GaN interlayers having different thicknesses

34. PL linewidth of GaN films inserted with LT-GaN interlayers having various thicknesses

35. Influence of low temperature AlN intermediate layers on the properties of GaN films

36. A schematic structure of GaN films having various LT-AlN interlayer thicknesses HT-GaN 0.9 m LT-AlN interlayer 25Å<d<125Å HT-GaN 0.6 m AlN buffer sapphire

37. RT PL spectra of GaN films inserted with AlN interlayers having different thicknesses

38. PL linewidth of GaN films inserted with LT-AlN interlayers having various thicknesses

39. Influence of low temperature AlGaN intermediate layers on the properties of GaN films

40. A schematic structure of GaN films having various LT-AlxGa1-xN interlayer thicknesses HT-GaN 0.9 m LT-AlxGa1-xN 25Å~200Å HT-GaN 0.6 m AlN buffer sapphire

41. RT PL spectra of GaN films having 2.5 nm-thick LT-AlGaN interlayers with different Al contents

42. RT PL spectra of GaN films having 5 nm-thick LT-AlGaN interlayers with different Al contents

43. RT PL spectra of GaN films having 7.5 nm-thick LT-AlGaN interlayers with different Al contents

44. RT PL spectra of GaN films having 10 nm-thick LT-AlGaN interlayers with different Al contents

45. PL linewidth of the GaN films versus the Al content of the 2.5 nm-thick LT-AlGaN interlayer

46. PL linewidth of the GaN films versus the Al content of the 5nm thick LT-AlGaN interlayer

47. PL linewidth of the GaN films versus the Al content of the 7.5nm thick LT-AlGaN interlayer

48. PL linewidth of the GaN films versus the Al content of the 10nm thick LT-AlGaN interlayer

49. RT PL spectra of GaN films inserted with different Al0.6Ga0.4N interlayers thicknesses

50. PL linewidth of GaN films inserted with LT-Al0.6Ga0.4N interlayers having various thicknesses