Exsitu Ohmic Contacts to nIn Ga As Prepared

Ex-situ Ohmic Contacts to n-In. Ga. As Prepared by Atomic Hydrogen Cleaning Ashish Baraskar 1, Mark A. Wistey 3, Evan Lobisser 1, Vibhor Jain 1, Uttam Singisetti 1, Greg Burek 1, Yong Ju Lee 4, Brian Thibeault 1, Arthur Gossard 1, 2 and Mark Rodwell 1 1 ECE and 2 Materials Departments, University of California, Santa Barbara, CA 3 Electrical Engineering, University of Notre Dame, In 4 Intel Corporation, Technology Manufacturing Group, Santa Clara, CA Issue: • In. P HBTs need contact resistivity (ρc) < 2 x 10− 8 Ω-cm 2 for ft and fmax >1 THz MJW Rodwell, Int. J. High Speed Electronics and Systems. 11, 159 (2007); MJW Rodwell , CSIC (2008) • ~10− 8 Ω-cm 2 ρc with in-situ contacts, but process flows often demand ex-situ contacts • Unpredictable native oxides; High temperature processing Fundamental Scaling Laws: To double device bandwidth: • Cut transit time 2 x: – Reduce thickness 2: 1 ☺ – Capacitance increases 2: 1 ☹ • Cut RC delay 2 x – Scale all resistivities by 4: 1 *M. J. W. Rodwell, IEEE Trans. Electron. Dev. , (2001); U. Singisetti, DRC (2007) Our Approach: • Surface preparation by atomic hydrogen cleaning • Increased doping Ashish Baraskar: University of California Santa Barbara PCSI-37

Ex-situ Ohmic Contacts to n-In. Ga. As Prepared by Atomic Hydrogen Cleaning Contact metal: Molybdenum (Mo) Experimental Details: • Highly doped n-In 0. 53 Ga 0. 47 As by solid source MBE • Surface exposed to air 20 nm Mo • Atomic hydrogen cleaning in MBE 100 nm In 0. 53 Ga 0. 47 As (n-doped) • Surface observed under RHEED before metal deposition 100 nm In 0. 52 Al 0. 48 As (NID) In. P (semi-insulating) • Transmission Line Model (TLM) for contact resistance measurement Experimental Results with Mo Contact Metal Process Surface Preparation ρc (Ω-µm 2) ρh (Ω-µm) In-situ As grown 1. 0± 0. 6 4. 3± 2. 6 Ex-situ (air exposure) H clean (MBE) 1. 3 ± 0. 5 5. 2 ± 3. 0 Dil. HCl 2. 3 ± 1. 0 9. 0 ± 3. 4 • Electron concentration, n = 5 x 1019 cm-3 • Mobility, µ = 770 cm 2/Vs • Sheet Resistance, Rsh = 15 ohm/□ (100 nm thick film) H cleaned (MBE) contacts are comparable to in-situ contacts Ashish Baraskar: University of California Santa Barbara PCSI-37

Ex-situ Ohmic Contacts to n-In. Ga. As Prepared by Atomic Hydrogen Cleaning Thermal Stability: • Contacts annealed under N 2 flow at 300 and 400 o. C for 1 minute duration • Low resistivity maintained after anneal: (1. 3 ± 0. 5) × 10 -8 Ω-cm 2 Conclusions: • Atomic hydrogen effectively cleans air-exposed semiconductor surfaces • ρc ~ (1. 3 ± 0. 5) Ω-µm 2 for atomic hydrogen cleaned Mo-n. In. Ga. As contacts • Contact resistivity comparable to in-situ Mo-n. In. Ga. As contacts • Mo contacts are thermally stable on In. Ga. As up to 400 o. C ü Contacts suitable for THz transistors Poster No: We 1645 Acknowledgements ONR, DARPA-TFAST, DARPA-FLARE Ashish Baraskar: University of California Santa Barbara PCSI-37