Femtosecond studies of surface electron transfer process at semiconductor interfaces

Technical Report · Mon Jan 01 04:00:00 EST 1990

OSTI ID:5939738

Miller, R J.D.

The primary focus of this research was to develop new spectroscopies applicable to the study of carrier dynamics at semiconductor surfaces. The progress made during the tenure of this grant includes the development of three novel techniques for surface studies: Surface Restricted Transient Grating Spectroscopy, Surface Acoustic Wave (SAW) spectroscopy, and Surface Space-charge Electro-optic Sampling. Further, these techniques were then applied to the study of carrier dynamics at n-TiO{sub 2} and n-GaAs interfaces. The primary results were that hole carrier reaction dynamics at TiO{sub 2} surfaces involves thermalized hole carriers at the surface on 100 psec time scales. A large effective hole mass of TiO{sub 2} is found m{sub h} greater than 3m{sub e} which negates any possibility of hot hole transfer. In contrast, the studies at n-GaAs (100) surfaces found hole carrier transfer to be faster than 30 psec and appears to be direct, without the intermediacy of surface states. The hole carrier transport to the surface is found to be faster than 300 fsec and approaches the ballistic limit for transport. Therefore, the hole carriers do arrive with large amounts of excess energy at the surface. These results indicate that at least some fraction of the hole carriers are transferring unthermalized. The importance of this in solar energy collection is that this work supports, at least from a fundamental standpoint, the possibility of exploiting hot carriers to avoid thermal energy loss mechanisms and enhance conversion efficiency. These studies are the first to provide direct time resolved (not diffusion limited) studies of surface reaction dynamics. In addition, the approach provides the highest possible resolution for studying surface reactions in the time domain. The specific results for both TiO{sub 2} and GaAs surface will be discussed below. 32 refs., 1 fig.

• Research Organization: Rochester Univ., NY (USA)
• Sponsoring Organization: DOE; USDOE, Washington, DC (USA)
• DOE Contract Number: FG02-85ER13455
• OSTI ID: 5939738
• Report Number(s): DOE/ER/13455-4; ON: DE91010914
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
140500 -- Solar Energy Conversion
36 MATERIALS SCIENCE
360603* -- Materials-- Properties
ARSENIC COMPOUNDS
ARSENIDES
BAND THEORY
CHALCOGENIDES
CHARGE CARRIERS
CHARGE TRANSPORT
CONVERSION
DOCUMENT TYPES
ELECTRON TRANSFER
ENERGY CONVERSION
ENERGY LOSSES
GALLIUM ARSENIDES
GALLIUM COMPOUNDS
HOLES
INTERFACES
LOSSES
MATERIALS
N-TYPE CONDUCTORS
OXIDES
OXYGEN COMPOUNDS
PNICTIDES
PROGRESS REPORT
RESEARCH PROGRAMS
SEMICONDUCTOR MATERIALS
SOLAR ENERGY CONVERSION
SPECTROSCOPY
SURFACE PROPERTIES
TITANIUM COMPOUNDS
TITANIUM OXIDES
TRANSITION ELEMENT COMPOUNDS