Work function contrast and energy band modulation between amorphous and crystalline Ge2Sb2Te5 films

Abstract

The work function (WF) is of crucial importance to dominate the carrier transport properties of the Ge-Sb-Te based interfaces. In this letter, the electrostatic force microscopy is proposed to extract the WF of Ge2Sb2Te5 (GST) films with high spatial and energy resolution. The measured WF of as-deposited amorphous GST is 5.34 eV and decreases drastically after the amorphous GST is crystallized by annealing or laser illumination. A 512 × 512 array 2D-WF map is designed to study the WF spatial distribution and shows a good consistency. The WF contrast between a-GST and c-GST is ascribed to band modulation, especially the modification of electron affinity including the contribution of charges or dipoles. Then, the band alignments of GST/n-Si heterostructures are obtained based on the Anderson's rule. Due to the band modulation, the I-V characteristics of a-GST/Si heterojunction and c-GST/Si heterojunction are very different from each other. The quantitative relationship is calculated by solving the Poisson's equation, which agrees well with the I-V measurements. Our findings not only suggest a way to further understand the electrical transport properties of Ge-Sb-Te based interfaces but also provide a non-touch method to distinguish crystalline area from amorphous matrix with high spatial resolution.

Engineering Interface-Dependent Photoconductivity in Ge2Sb2Te5 Nanoscale Devices

“…On the basis of the above observations we therefore conclude that the photoresponse we observe is due to a photo-voltaic effect in our devices. It is likely driven by the existence an asymmetric built-in electric field from Schottky barriers at the GST/ITO interfaces ( and arising from the differences in the work function (Φ) of GST and ITO 36,37 between electrodes made from same material) 38,39 . Based on our results, we deduce the photocurrent mechanism as illustrated in Figure 4A and B for the amorphous and crystalline states of GST respectively.…”

CMOS compatible novel integration solution for broad range tunable photodetection using phase-change material based heterostructures

“…where, A is the effective area (~ 0.3 mm 2 ), A * Richardson constant defined as 4πqm * k 2 /h 3 (m * is effective mass and taken as 1.52m 0 for majority carriers in GST 59 ) and φ is the barrier height. The barrier height can be calculated from Eq.…”

“…9a,b. The measurement methodology and setup are adopted from Tong et al 59 and Monu et al 14 . To avoid topographic artifact, dual pass taping mode was employed.…”

“…The position of Fermi-level (E F ) with respect to valance-band (E v ) can be calculated by the Fermi-Dirac distribution function as given in Eq. 7: www.nature.com/scientificreports/ There are still a lot of disputes on the location of E F for CGST as every method of depositions/mechanisms and substrate yields in different Fermi position but it is more accepted as p-type degenerate semiconductor 45,59 . Also, from the huge carrier-concentration, we are assuming it as degenerate semiconductor and Fermi-position of CGST can be estimated by Eq.…”

“…Also, the photo-generated carriers in Si arising from the absorption also contribute to the photo-current and hence increasing the performance parameters. Furthermore, the asymmetric band offset with Si valance-band (VB)/conduction-band (CB) will offer an efficient collection/rectification of charge carriers 59 and constitute low reflective losses as the refractive indices of both are compatible 60 . Miller et al 61 have carried out the electro-optical characteristic of optically induced phase change material (O-PCM) integrated with Si only at 2 μm wavelength.…”