An#- Phase- Boundary Defects in GaAs- on- Si Films: 1. characteriza#on by SHG 2. suppression by ART

Transcription

1 Op=cs of Surfaces & Interfaces (OSI - 9) Chemnitz, Germany September 2, 213 An#- Phase- Boundary Defects in GaAs- on- Si Films: 1. characteriza#on by SHG 2. suppression by ART Farbod Shafiei 1, Ming Lei 1,2 Man- Hoi Wong 3 and Mike Downer 1 1 University of Texas at Aus2n 2 GlobalFoundries, Inc. 3 Sematech and Intel Corp. The microelectronics industry is trying to marry III-V and Column IV semiconductors via hetero-epitaxy to combine the favorable properties of each High mobility FETs Efficient solar cells III- V nanolasers on thermal Si (Intel 29) >5% GaAs e mobility Direct GaAs InGaAs (cm 2 shell conduc#vity core /V s) gap (W/cm oc) InGaP 4% GaAs InGaAs Si InGaP ~15% ~3% GaAs Si Si GaAs Ge Ge single junc=on mul=- junc=on GaAs Si 85 Y.55 Si 13 N 1.3 Chen, Nat. Phot. 5, 17 (211) 5 nm

2 GaAs/Si interfaces are suscep#ble to forma#on of defects Threading Disloca#ons (TDs) Where: any hetero- interface Cause: lasce mismatch misfit dislocation Characteriza#on: selec#ve etching + TEM GaAs/Si(1) 3 µm Hsu, Nanotech. 23, (212) substrate TDs misfit disloca=on sub- strate Si (1) Ge (1) [1] lasce mismatch w. GaAs [1] [1] typical TDD [cm - 2 ] 4% >1 9 <1% <1 8 An#- Phase Domains (APDs) Where: polar- on- nonpolar hetero- interfaces Cause: single- atom steps, nonpolar substrate ( ) Kawabe, JJAP 26, L944 (1987) Ga- Ga bonds along An#- Phase Boundaries (APBs) degrade carrier mobility TEM 1 µm Brammertz, TSF 517, 148 (28) To evaluate strategies for suppressing these defects, a fast, noninvasive diagnos#c that clearly dis#nguishes APBs from TDs is needed As Ga Si TDs and APBs are chall- enging to dis#nguish in TEM micrographs

3 Neighboring APDs generate SH fields of opposite sign Destruc=ve interference in far field Incident fundamental field E(ω) +E(2ω) - E(2ω) +E(2ω) SH escape depth +χ (2) - χ (2) +χ (2) Previous related work: Amzallag, APL 66, 982 (1995)

4 SHG characterizes APBs sensi#vely and non- invasively α s!! E in p ϕ GaAs(1) Si(1) 2ω epi- GaAs grown by MBE TEM laser spot ~ 3 µm 1 µm APDs:.1 2 µm SHG signal (arb. u.) sample azimuthal rota#on (p- in/s- out) GaAs(1) GaAs/Si(1) Azimuthal angle ϕ (deg) I s (2ω) α sin2ϕ 2 [Yamada. Phys. Rev. B 49, (1994)] 2 1 SHG signal (arb. u.) incident polariza#on rota#on (ϕ = 22.5 o ) GaAs(1) GaAs/Si(1) Polariza=on angle α (deg) I s (2ω) α cosα(f c t p cos2ϕ cosα + t s sin2ϕ sinα) 2 2 1

5 To test SHG sensi#vity to TD Density (TDD), we prepared In x Ga 1- x As/GaAs samples 2 x = x =.5 x =.75 x =.11 x =.3 1 Integrated SHG Intensity [1 4 cts/s] 18 o 36 o 18 o 36 o 18 o 36 o 18 o 36 o 18 o x = Indium content.2 lagce mismatch 1 8 TDD [cm - 3 ] 1 9 Conclusion: SHG is uncorrelated with TDD 36 o p- in/p- out s- in/p- out

6 Substrate off- cut angle α strongly affects APD density & SHG suppression TEM GaAs/Si(1) 1 SHG signal (arb. u.) As GaAs/Si: α = 4o No APBs evi- dent by TEM 5 Avg. APD size:.3 µm 1 µm 4 GaAs/Ge: GaAs/Ge(1) (smaller α) α = 6o 1 2 Avg. APD size:.8 µm 1 µm Azimuthal angle φ (degrees) Azimuthal angle φ (degrees) GaAs <SHG intensity> 1 Roughness nm.9 TDD /cm- 2 N/A GaAs/Si(1) GaAs/Ge(1) GaAs/Si: 4o GaAs/Ge: 6o x 1-3cm TDD: RMS roughness: 5.8 nm Ga APDs suppressed, SHG recovers SHG suppression correlates with APD density GaAs(1) Si α 4o: double- atom steps dominate; α < 1o: single- atom steps dominate;

7 Scanning SHG microscope yields mohled SHG response from APD- laden surfaces Lei et al., APL 12, (213) ω 2ω St. Dev. of SHG intensity GaAs/GaAs GaAs/Si(1) 1 µm 1 µm sample rastered in focal plane The SHG images are NOT direct maps, but rather higher- order moments, of the APD distribu=on. Bright areas indicate dominance of one type of domain within the laser spot. GaAs/Ge(1): 6 o.37 1 µm.26 GaAs/Ge(1) Dark areas indicate equal areas of +χ (2) and χ (2) domains within the laser spot. SHG NSOM* may be able to image individual APDs directly. ω NSOM =p 5 nm *Smolyaninov, Phys. Rev. B 56, 929 (1997) Bozhevolnyi, Opt. Commun. 15, 49 (1998)

8 Growth of GaAs on exactly oriented Si(1) is preferred for high- volume manufacturing Aspect- Ra=o Trapping (ART) is an established technique for suppressing TDs on Si(1) [11] SiO 2 trench walls Si(1) 3D geometry: Fitzgerald, J. Electron. Mater. 2, 839 (1991) trapped TDs a b GaAs 1 nm [11] trench sidewall TD- free region All TDs trapped for b/a > 2 We found (serendipitously) that ART pawerning of oriented Si(1) substrates also drama#cally suppresses APDs in GaAs epi- films SHG signal [arb. u.] 1 GaAs ref. ART GaAs/Si(1) Incident polariza=on angle α 1 GaAs/Si(1) [11] trench sidewall Nearly complete recovery of GaAs reference SHG signal!

9 GaAs pillars evidently coalesce commen- surately into a single domain epi- layer {111} facets tapered sidewall with pliable Si- O bonds may encourage Ga- As bond forma=on when pillars merge TDs ART appears to solve 2 problems simultaneously!

10 SUMMARY SHG characterizes APDs in polar- on- nonpolar semiconductor epi- films sensi=vely, quickly, non- invasively and selec=vely. Scanning SHG microscopy indirectly probes APD size distribu=on; SHG- NSOM promises direct APD imaging. SHG APD probe helps develop methods to suppress APDs: e.g. 1. vicinal substrates; 2. ART Compared to RAS, SHG is equally useful as an ex- situ & in- situ APB probe, requires only a single- λ source for any material system, and enables microscopic (possibly single APD) imaging. Lei et al., Appl. Phys. Lett. 12, (213) Patent Pending Financial Support from: Robert Welch Founda=on U. S. Na=onal Science Founda=on