Digging up bulk band dispersion buried under a passivation layer

Abstract

Atomically controlled crystal growth of thin films has established foundations of nanotechnology aimed at the development of advanced functional devices. Crystallization under non-equilibrium conditions allows engineering of new materials with their atomically-flat interfaces in the heterostructures exhibiting novel physical properties. From a fundamental point of view, knowledge of the electronic structures of thin films and their interfaces is indispensable to understand the origins of their functionality which further evolves into realistic device application. In view of extreme surface sensitivity of the conventional vacuum-ultraviolet (VUV) angle-resolved photoemission spectroscopy (ARPES), with a probing depth of several angstroms, experiments on thin films have to use sophisticated in-situ sample transfer systems to avoid surface contamination. In this Letter, we put forward a method to circumvent these difficulties using soft X-ray (SX) ARPES. A GaAs:Be thin film in our samples was protected by an amorphous As layer with an thickness of $\sim 1$ nm exceeding the probing depth of the VUV photoemission with photon energy $h\nu$ around 100 eV. The increase of the probing depth with increasing $h\nu$ towards the SX region has clearly exposed the bulk band dispersion without any surface treatment. Any contributions from potential interface states between the thin film and the amorphous capping layer has been below the detection limit. Our results demonstrate that SX-ARPES enables the observation of coherent three-dimensional band dispersion of buried heterostructure layers through an amorphous capping layer, breaking through the necessity of surface cleaning of thin film samples. Thereby, this opens new frontiers in diagnostics of authentic momentum-resolved electronic structure of protected thin-film heterostructures.Comment: 5 pages, 3 figure

Unveiling the impurity band induced ferromagnetism in the magnetic semiconductor (Ga,Mn)As

“…S1 and S2, and the movie in the Supplemental Material [23]). Details of the SX-ARPES experiment illustrating its penetrating ability through capping As layers have been published elsewhere [24]. These results exclude any possible surface As capping layer or (Ga,Mn)As/As interface contributions in our ARPES spectra.…”

Doping-dependent band structure of LaAlO3/SrTiO3interfaces by soft x-ray polarization-controlled resonant angle-resolved photoemission

“…Photoemission spectroscopy of buried interfaces is more challenging due to the small inelastic electron mean free path in solids, which, over a wide range of photon energies (hν), is of the order of 1 nm. However, it was shown recently that a combination of soft x-ray photoemission with resonant photoexcitation [14][15][16][17][18] can overcome this limitation. By selecting hν at the Ti L edge, the signal of the Fermi states associated with conducting electrons is greatly enhanced in LAO/STO interfaces.…”

Minority-spin impurity band in n -type (In,Fe)As: A materials perspective for ferromagnetic semiconductors

“…The underlying physics of the formation of the split-off IB is found to be similar to that in p-type (Ga,Mn)As [17], suggesting a unified picture for realizing carrier-induced ferromagnetism in FMSs irrespective of the carrier types. The intensity of band dispersion depends on the polarization of the incident x rays reflecting the matrix element effects [37] and symmetry of the bands: The LH and SO bands, and CBM of the host InAs can be observed with p polarization, and the heavy-hole (HH) band with s polarization, as well as the polarization dependence of bands of GaAs [23,38] (note, however, that the CBM of GaAs has not been observed in the previous study because E F is located below the CBM in p-type GaAs). Figure 5 shows the ARPES spectrum along the -K-X symmetry line taken with the s polarization.…”