金氧半光偵測器 Novel Metal-Insulator-Semiconductor Photodetector

1. 金氧半光偵測器Novel Metal-Insulator-Semiconductor Photodetector • 指導教授：劉致為 博士 • 學生：郭平昇 • 台灣大學電子工程學研究所

2. Introduction • LPD Oxynitride • Recessed Oxynitride Dots on Self-assembled Ge Quantum Dots • Ge/Si Quantum Dot MOS Photodetectors for Optical Communication • MIS Ge/Si Quantum Dot Infrared Photodetectors (QDIP) (intraband transition) • A Dual-polarity Operable MOS Photodetector with Pt Gate (interband transition) • Summary Outline

3. The electro-optical products may be one of the killer applications in the future Si market. • The worldwide revenue of the optical semiconductor is ~5 % (~7 B) of the total semiconductor revenue (~140 B) 2002. • (Note RF: 4.7 B, MEMS : 4.6 B) • The ITRS has predicted that the incorporation of optoelectronic components into CMOS-compatible process is needed to achieve System-on-a-Chip. • CMOS optoelectronics: OE Devices fabricated by CMOS available technology Introduction

4. Si-based CMOS optoelectronics • - low cost, high reliability, VLSI compatible Introduction Electrical Parts Optical Parts

5. Introduction • Ge mole fraction   cut-off wavelength  absorption length 

6. NMOS detector response • Al gate • Zero bias • Cut-off wavelength = 1.18m • Ecutoff = 1.05 eV < Ebandgap • Phonon-assistant absorption (65 meV)

7. LPD Oxynitride Process flow of LPD oxynitride. The proposed LPD-SiON mechanism.

8. The LPD-SiON has a lower • current than the LPD-SiO2. Accumulation region Inversion region

9. Recessed Oxynitride Dots on Self-assembled Ge Quantum Dots (a) Oxynitride (b) Oxide

10. Tensile Strain : • The Si cap area above the Ge dots has a tensile strain, and the Si cap area on Ge wetting layers is strain free. • The tensile strain can enhance the oxynitride deposition rate on the strained Si on SiGe 20% buffers.

11. SIMS profile of Oxynitride O:N = 16:7 at the interface Recess the top Ge dot

12. Dot Height • The LPD-SiON has a higher deposition rate as compared to the LPD- • SiO2, and the deposition rate increases as ammonia concentration • increases. • Under the same wetting layer thickness, the LPD-SiON dots still yield • a higher dot height.

13. AFM Morphologic: Quantum Dot  AFM surface image and Cross- section morphologyof LPD oxide with 15 nm wetting layer thickness.  AFM surface image and Cross- section morphologyof LPD oxynitride (1M NH4OH) with 15 nm wetting layer thickness.

14. Quantum Ring Depostion time : (a) 12 min (b) 20 min. • The tensile strain area can have preferential oxide • deposition. • The LPD-SiO2 deposited on quantum ring sample • acts just like the stalactite.

15. Ge Quantum Dots • 5 ~ 20 layer self-assembled Ge quantum dots • prepared by UHVCVD under SK growth mode.

16. LPD vs. RTO (700 oC) • Devices with LPD oxide have higher efficiency.

17. Device Operation • I-V curves at 820 nm (device area = 3x10-4 cm2)

18. Device Operation • Carriers can tunnel through oxide via the assistance of multiple traps.

19. Results and Discussion • Dark current of all 4 devices. • The dark current of 5-layer QD device  0.06 mA/cm2

20. 820 nm • Efficiency of 5-layer Ge QD device  20%

21. 1300 nm • Efficiency : 5-layer Ge QD (0.16 mA/W) > • multi-layer Si0.8Ge0.2 (0.04 mA/W)

22. 1550 nm • Only Ge and 5-layer Ge QD detectors have response.

23. Optimized QD Structure • Optimize number of periods and Si • spacer layer thickness. • Number of periods •  5, 10, 20 periods • Si spacer thickness •  20 nm, 50 nm

24. High Efficiency at 850 nm • 20 - period QDs, 50 nm spacers • High responsivity at 850 nm  0.6 A/W

25. Discussion • Quantum dot periods   Responsivity  • Si spacer thickness   dark current ↓ ( x 10-3 ) • For 20-period QDs, 50 nm spacers - High responsivity 0.6 A/W at 850 nm - Low dark current 0.3 mA/cm2

26. Quantum dot infrared photodetector (QDIP) • => low dark current, high operation temperature and normal incident detection • Applications => military, medical, astronomical and many others. • The MOS structure with tunneling insulator can make the Ge/Si QDIP • => small dark current • compatible with Si ULSI process MOS Ge/Si QDIP( intraband transition)

27. Grown by UHVCVD Device Fabrication • The base width and height of the Ge dots are ~100 nm and • 6~7 nm, respectively. The Ge dot density is ~1010 cm-2

28. Device Fabrication • Dark current is limited by minority generation rate (from Dit and bulk traps). • The confined holes have transitions under infrared exposures.

29. PL spectrum => QD barrier 0.3~0.4 eV Discussion

30. Smaller dark current duo to lower Dit Device Performance

31. The operating temperature reaches 140 K for 3~10μm detection. Device Performance

32. 2~3 μm response up to 200 K • large response at short wavelength => interband transition Device Performance

33. Peak Detectivity @ 100 K ~ 1010 cmHz0.5/W Device Performance

34. The normalized detectivity D* is defined as: • A is the detector area, Δf is the equivalent bandwidth of the electronic system, and NEP = in/R is the noise equivalent power. The in is current noise and R is the responsivity. • The current noise is limited by the dark current and can be approximated as the shot noise (2eIdΔf)1/2, where Id is the measured dark current. Device Performance

35. A Dual-polarity Operable MOS Photodetector with Pt Gate (interband transition) • The quantum dot device has lower current as compared to the Si device both in accumulation and inversion region due to hole blocking effect.

36. Photo I-V • The Q.D device with Pt gate has photo-response under accumulation region due to Pt has larger workfunction 5.3 e.V ( high electron barrier = 4.3 eV ). Al has lower barrier : 3.1 eV.

37. Pt & Al • For Al gate device, quantum dot has higher inversion current than Si due to Ge dot has a smaller bandgap. • There is a inverse trend for Pt gate device due to hole blocking effect.

38. Low Temperature photo I-V of Ge quantum dot device Extra electron current from Pt gate Photo generated electron current in depletion region No depletion region, low photo current

39. Hole blocking at low temperature • Hole blocking effect is more severer at low temperature.

40. Conclusion • The tensile strain on the Si cap above self-assembled quantum dots can probably enhance the etching rate of Si and have a preferential oxynitride deposition on the Ge dots during LPD process. • Due to the N atoms passivation of the interface states, the device with oxynitride yields a lower dark current as compared to oxide device. • The MOS Ge/Si QDIPs for 2 ~ 10 μm using hole inter-valance subband transitions are successfully demonstrated. The maximum operating temperature is 140 K for 3 ~10 μm and is up to 200 K for 2 ~ 3 μm detection with LPD oxynitride.

41. Conclusion • The MOS Ge quantum dot devices can • have high responsivity (0.6 A/W at 850 nm) • and low dark current. • Oxide is grown by LPD and Ge quantum • dot structures are prepared by UHVCVD. • MOS Ge quantum dot devices • Si spacer thickness • dark current↓( x10-3 ) • The NMOS Ge quantum dot photodetector with Pt gate • can be operated in both inversion and accumulation • regions. The valence bandoffset in Si/Ge • heterojunction can confined the hole and form a • energy barrier to block the hole current.