Phase-change films with multiple resistance levels are promising for increasing the storage density in phase-change memory technology. Diffusion-dominated Zn₂Sb₃ films undergo transitions across three states, from high through intermediate to low resistance, upon annealing. The properties of the Zn₂Sb₃ material can be further optimized by doping with Bi. Based on scanning transmission electron microscopy combined with electrical transport measurements, at a particular Bi concentration, the conduction of Zn-Sb-Bi compounds changes from p- to n-type, originating from spinodal decomposition. Simultaneously, the change in the temperature coefficient of resistivity shows a metal-to-insulator transition. Further analysis of microstructure characteristics reveals that the distribution of the Bi-Sb phase may be the origin of the driving force for the p–n conduction and metal-to-insulator transitions and therefore may provide us with another way to improve multilevel data storage. Moreover, the Bi doping promotes the thermoelectric properties of the studied alloys, leading to higher values of the power factor compared to known reported structures. The present study sheds valuable light on the spinodal decomposition process caused by Bi doping, which can also occur in a wide variety of chalcogenide-based phase-change materials. In addition, the study provides a new strategy for realizing novel p–n heterostructures for multilevel data storage and thermoelectric applications.

Due to the intrinsic contradiction of electrical conductivity and Seebeck coefficient in thermoelectric materials, the enhancement for the power factor (PF) is limited. Since the PF decides the output power, strategies to the enhancement of PF are of paramount importance. In this work, Bi₂Te₃/Sb and Bi₂Te₃/W multilayer films are proposed to enhance the thermoelectric properties. Both systems possess extremely high conductivity of ≈5.6 × 10⁵ S m⁻¹. Moreover, the electrical conductivity and Seebeck coefficient simultaneously increase as temperature rising, showing the overcome of the intrinsic contradiction. This results in ultrahigh PFs of 1785 µWm⁻¹ K⁻² for Bi₂Te₃/W and of 1566 µWm⁻¹ K⁻² for Bi₂Te₃/Sb at 600 K. Thermal heating of the Bi₂Te₃/Sb multilayer system shows compositional changes with subsequent formation of Bi‐Te‐Sb phases, Sb‐rich Bi‐Te precipitates, and cavities. Contrary, the multilayer structure of the Bi₂Te₃/W films is maintained, while Bi₂Te₃ grains of high‐crystalline quality are confined between the W layers. In addition, bilayer defects in Bi₂Te₃ and smaller cavities at the interface to W layers are also observed. Thus, compositional and confinement effects as well as structural defects result in the ultrahigh PF. Overall, this work demonstrates the strategies on how to obtain ultrahigh PFs of commercial Bi₂Te₃ material by microstructure engineering using multilayer structures.

Reconfigurable silicon photonic devices attract much research attention, and hybrid integration with tunable phase-change materials (PCMs) exhibiting large refractive index contrast between amorphous (Am) and crystalline (Cr) states is a promising way to achieve this goal. Here, we propose and numerically investigate a S b 2 S e 3 -Si hybrid waveguide Bragg filter operating in the telecom C-band on the silicon-on-insulator (SOI) platform. The proposed device consists of a Bragg grating (BG) with a thin top layer of ultralow-loss S b 2 S e 3 PCM interacting with evanescent field of the silicon waveguide mode. By harnessing the ultralow-loss and reversible index change of S b 2 S e 3 film, the spectral response of the hybrid BGs could be dynamically tuned. We also theoretically investigate the reversible phase transitions between Am and Cr states of S b 2 S e 3 film that could be attained by applying voltage pulses on the indium-tin-oxide (ITO) strip heater covered on S b 2 S e 3 film. Thermal simulations show that a 2 V (4.5 V) pulse with a duration of 400 ns (55 ns) applied to electric contacts would produce crystallization (or amorphization). The proposed structure may find great potential for on-chip phase tunable devices on a silicon platform.

Elemental antimony (Sb) has been carried out recently as a phase-change material to overcome composition segregation in a heavily cycled memory cell. Explosive crystal growth of Sb is desirable for fast operation speed in memory; however, poor thermal stability, i.e., fast spontaneous crystallization at room temperature, significantly impedes its applications. In this work, we designed a thermal stability enhanced “monatomic” Sb in a specific confined structure of [Sb(3 nm)/SiO₂(5 nm)]₃₂ and investigated its crystallization kinetics by using the ultrafast differential scanning calorimetry method. It was found that this nanoscale Sb exhibits appealing amorphous thermal stability with a crystallization activation energy of 2.68 eV and the temperature for 10-year data retention more than 361 K. Moreover, strong non-Arrhenius crystallization behavior with a high fragility index of 90 was unrevealed in Sb supercooled liquids, which has the maximum crystal growth rate of 2.17 m s⁻¹ at 785 K. Thanks to the fast crystal growth rate and attractive thermal stability of this monatomic Sb, it could be one of the most important candidates for high-integrated on-chip memory without any composition segregation.