Semiconductor Nanostructures

Transcription

1 II H. von Känel Laboratorium für Festkörperphysik ETHZ

2 Applications Lighting Field effect transistors Sensors Infrared sensors X-ray detectors

3 Periodic table of elements

4 Comparison of wurtzite and zinc- blende structures

5 Group III-nitrides Structural data Fundamental band gaps (direct)

6 Band structures of AlN, GaN and InN All direct bandgap Semiconductors! Ph.D thesis Alexander Vozny Chernivski Natl. Univ., Ukraine 2004

7 Variation of bandgap with lattice parameter UV-green group III nitrides Yellow-red zinc blende arsenides - phosphides p M.R. Krames et al., J. Display Technol. 3,, 160 (2007)

8 LED chip designs M.R. Krames, J. Display Technol. 3,, 160 (2007)

9 p-n junctions at equilibrium and forward bias (a) (b) (c)

10 Osram s s blue LED chips 1 1 mm 2 chip size 350 ma drive current B. Hahn et al., Proc. SPIE Vol (2008)

11 GaN PL intensity vs. TDD Theory: J.H. You, J. Appl. Phys. 101,, (2007)

12 Efficiency droop InGaN/GaN QW-based 1 1 mm 2 TFFC chips M.R. Krames et al., J. Display Technol. 3, 2007)

13 Time resolved PL of thick alloys S. Chichibu, nature materials 5, 810 (2006)

14 Inversion eso domains formation ato in GaN M. Stutzmann et al. phys. stat. sol. (b) 228, 505 (2001) Domain formation due to nucleation of Ga-face and N-face grains Need well-defined nucleation step

15 Al 2 O 3 surface termination and polarity Epi-ready sapphire is O-terminated O-removal during High-T thermal treatment M. Stutzmann t et al., phys. stat. t sol. (b) 228,, 505 (2001)

16 PL in In-containing alloys Spatially varying energy of excited state due to atomic-scale inhomogeneity Stokes shift between absorption and emission

17 Polarization of strained and unstrained nitrides O. Ambacher et al., J. Appl. Phys. 85,, 3222 (1999)

18 Polarization and band profiles Left image: Polar (0001) oriented heterostructure Right image: non-polar a-face orientation S. Chichibu, nature materials 5, 810 (2006)

19 GaN columns on AlN/Si(111) Potential for columnar LEDs with much higher light extraction ti efficiency i

20 Sensitivity of the human eye Green: night vision Gray: day vision

21 CIE chromaticity diagram CIE = Commission Internationale de l Eclairage

22 Blue-pumped YAG phosphor R Pump wavelength 460 nm LER decreases with blue leakage! M.R. Krames, J. Display Technol. 3,, 160 (2007)

23 Chromaticity for blue-pumped YAG y CCT ~ 5000 K for 35 % blue leakage (LER = 328 lm/w) Theoretical maximum LES ~ 283 lm/w at CRI ~ 80 M.R. Krames, J. Display Technol. 3,, 160 (2007)

24 Maximum down-conversion efficiency CE=(P leak +P conv )/P )/P LED M.R. Krames et al., J. Display Technol. 3, 160 (2007)

25 Near band edge PL of alloys S. Chichibu, nature materials 5, 810 (2006)

26 Quantum efficiencies of HBLEDs J.M. Phillips, Laser & Photon Review 1, No. 4, 2007

27 Maximum LER for RYGB (CCT = 3000 K) All linewidths 1 nm CCT = 3000 K JM J.M.. Phillips et al., Laser & Photon Rev. 1, 307 (2007)

28 Scheme of GaN-HEMT

29 Sheet charge density at AlGaN/GaN interfaces O. Ambacher et al., J. Appl. Phys. 85, 3222 (1999)

30 Al Al 0.09 Ga Ga 0.91 N/GaN heterostructure Sheet electron density Mobility cm 2 /Vs at 4 K cm -2 at 4 K 12 cm C.R. Elsass et al., Jap. J. Appl. Phys. 39, L1023 (2000)

31 Comparison of HEMTs F. Schwierz, TU Ilmenau 2003

32 Comparison of transport properties p Typical room temperature data for important interfaces

33 Band structures of Si, Ge and α-sn Empirical pseudopotential method, Chelikowski and Cohen 1976

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35 Band structures of tetrahedrally bonded d semiconductors Note the close similarity of the Ge band structure with that of GaAs around Γ

36 Ge under biaxial ba a strain M.V. Fischetti & S.E. Laux, J. Appl. Phys. 80, 2234 (1996)

37 Improved hole transport: compressive strain unstrained E compressively strained E k k LH SO HH Strain lifts HH-LH degeneracy Heavy holes become lighter Anti-crossing with LH band leads to non-parabolicity

38 Modulation doped strained Ge quantum wells Typical structure used for high mobility hole transport t

39 Record hole mobility of Ge quantum well B. Rössner et al., APL 84,, 3058 (2004) Most recently (University of Warwick 2012) > cm 2 /Vs!

40 Ge photodiodes for IR detection Band gap shift by thermally induced tensile strain in Ge on Si

41 Bandgap shift through thermal annealing Extraction of the direct band-gap energy for the as grown ( ) and annealed ( ) 1 µm thick absorption layer G. Isella et al., Semicond. Sci. Technol. 22,, S26 (2007)

42 CMOS-integrated pixel detector CMOS circuit 2.5 µm, 1 metal, 1 poly process of CNM Barcelona R. Kaufmann et al., JAP 110, (2011)

43 IR image sensor with integrated Ge photodetectors R. Kaufmann et al., JAP 110, (2011)

44 Absorbed photons vs. X-reay tube voltage

45 Current-voltage measurements Au wire A p-si p-ge Ge Ge Ge n-si

46 In-situ measurements in SEM-chamber SEM chamber SEM picture of top contact on individual germanium tower tungsten tip A p-si p-ge I d Ge Ge Ge V d 2 µm Conductive tungsten tip n-si I-V characteristics measured in-situ SEM Zeiss Nvision µm

47 Definition of detector pixels H. von Känel, Europhysics News 43,, 18 (2012)