Electronic structure of technologically important interfaces and heterostructures
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Prospective Article
Electronic structure of technologically important interfaces and heterostructures Richard Haight, IBM TJ Watson Research Center, PO Box 218, Yorktown Heights, NY 10598, USA Address all correspondence to Richard Haight at [email protected] (Received 13 June 2020; accepted 11 August 2020)
Abstract From thin film solar cells to metal–oxide–semiconductor (MOS) devices in leading edge integrated circuits, the electronic structure at and near the interfaces between component materials determines the most important fundamental operating characteristics of those devices such as turn-on voltage, power dissipation, and off-state current leakage. Fermi level location at buried interfaces, semiconductor (SC) band bending, charge transfer, oxide defects, and work functions of the constituent materials all contribute to device performance. This paper describes how these important parameters can be determined by employing femtosecond photovoltage spectroscopy, an extension of ultraviolet photoelectron spectroscopy (UPS) using ultrafast lasers. While standard UPS is fundamentally a surface-sensitive spectroscopy, pump/probe techniques add a new dimension to this venerable spectroscopy, permitting the accurate extraction of the underlying band bending in SCs. When combined with the valence band edge location of the SC and oxide, and determination of the system Fermi level, full characterization of the electronic structure of a MOS stack can be obtained providing key insights on device operating properties. This approach can be extended to study key device materials in emerging areas of artificial intelligence and quantum computing. In each case, surprising new details were uncovered that led to performance optimization of these technologically important devices.
Introduction Atomic and electronic structure are the two key interdependent drivers of performance in any functional electronic device. From the atomic structure inherent in a heterostructure formed between two dissimilar materials, either crystalline, amorphous, elemental or compound, or a combination of these, the electronic properties of a device and its resultant performance will be determined. Barriers to electronic flow between materials and across interfaces are strongly influenced by the fundamental electronic properties of the materials. These include energy barriers that permit electron flow in one direction but not the reverse, the existence of defects that can trap charge, scatter electrons, and more that will all conspire to determine the properties and performance of the device constituted from these materials. To understand the myriad electronic properties, a combination of established knowledge of the materials with additional new measurement modalities must be brought to bear, particularly as new material sets with ever greater complexity are utilized to achieve improved performance and unique new functionality. One well-established method to measure the electronic properties of materials such as the location of the Fermi level, work func
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