Evaluation of bias-dependent band structure changes in metal–oxide–semiconductor structures with varying doping concentrations using laboratory hard x-ray photoelectron spectroscopy

Direct observation of the band structure variation of electrical devices, such as MOSFETs, during device operation is the most important for understanding MOSFET device operation. However, there are a few reports on the direct measurement of variation in the metal–oxide–semiconductor (MOS) interface band structure during operation, and further investigation is required. This paper focuses on elucidating the changes in the band structure at buried interfaces under applied bias using a nondestructive approach. We conducted measurements using bias-applied laboratory hard x-ray photoelectron spectroscopy (Lab. HAXPES) with liquid gallium (Ga) x-ray source on MOS structures, which are widely recognized as fundamental and commonly used devices. We utilize HAXPES with Ga x-ray, providing high-energy/intensity x-rays, to achieve sufficient detection depth and enable observation of the deeper regions of the silicon substrate buried under gold and silicon dioxide layers. As a result, this approach allowed us to observe bias-dependent peak shifts resulting from changes in the band structure in detail. We observe HAXPES peak shift caused by the different substrate concentrations. Additionally, we obtained detailed information on band bending by applying a wider range of bias compared to previous bias applied HAXPES.