Jin-seo Noh

Observation of molecular nitrogen in N-doped Ge2Sb2Te5

Ge2Sb2Te5 (GST) film in the crystalline state was nitrogen doped using the reactive sputtering method in order to increase sheet resistance. High-resolution x-ray absorption spectroscopy revealed that molecular nitrogen (N2) existed in the N-doped GST film. This finding implies that both molecular nitrogen and atomic-state nitrogen should be taken into account in understanding the structures of N-doped GST film. The molecular nitrogen is believed to exist at interstitial and vacancy sites, and more likely at grain boundaries.

High-resolution x-ray photoelectron spectroscopy on oxygen-free amorphous Ge2Sb2Te5

Amorphous Ge2Sb2Te5 (a-GST) film, 100nm thick, was grown by cosputtering from GeTe and Sb2Te3 targets on a silicon wafer at room temperature. The native oxidized layer, which was formed in air and about 20nm thick measured by secondary ion mass spectroscopy, was removed by Ne+ ion sputtering for 1h with 0.6kV beam energy. Core-level spectra of the Te 3d and 4d, Sb 3d and 4d, and Ge 3d of the oxygen-free a-GST were obtained by high-resolution x-ray photoelectron spectroscopy with synchrotron radiation and compared with those from Ge and GeTe. The analysis implies that the a-GST is composed on the base of chemical states of GeTe.

Nonvolatile switching characteristics of laser-ablated Ge2Sb2Te5 nanoparticles for phase-change memory applications

Electrical characteristics of Ge2Sb2Te5 (GST) nanoparticles have been examined for a phase-change memory applications. The GST nanoparticles were generated by in situ pulsed laser ablation and their crystal structure formation was confirmed [H. R. Yoon et al., J. Non-Cryst. Solids 351, 3430 (2005)]. A stacked structure of the GST nanoparticles with 10nm of average diameter shows reversible nonvolatile switching characteristics between a high resistance state and a low resistance state as in the phase-change memory consisting of bulk GST thin film. Experimental results indicate that it is highly probable to test scaling issues of the phase-change memory with well-defined GST nanoparticles.

Critical Quenching Speed Determining Phase of Ge 2 Sb 2 Te 5 in Phase--Change Memory

During the phase-change process of Ge₂Sb₂Te ₅ in PRAM (phase-change random access memory), phase-change dynamics are strongly dependent on the quenching speed, i.e. the cooling speed of melted phase-change material. Here the paper reports the relation between quenching speed of programming pulse and phases of Ge ₂Sb₂Te₅ in phase-change memory in detail. The existence of critical quenching speed is identified, which determines amorphous and crystalline phases in melting followed by quenching operation

Experimental Setup for in Situ Investigation of Phase Changing Behavior in Phase-Change Random-Access Memory Medium by Microfocusing Nanosecond-Time-Resolved Ellipsometry

An ellipsometer with nanosecond time resolution has been proposed for the investigation of the phase change behavior of Ge2Sb2Te5 heated by electrical pulses of 20–100 ns in real time. This passive single-wavelength ellipsometer has a division-of-amplitude photopolarimeter (DOAP) configuration for polarization state detection to collect ellipsometric data in nanoseconds and consists of a microfocusing lens system to achieve a spot size of ~15 µm.

Electronic structure of (Ge2Sb2Te5)1−x(In3SbTe2)x investigated by x-ray photoelectron spectroscopy

We have investigated the core levels and the valence band of (Ge2Sb2Te5)1−x(In3Sb1Te2)x quaternary phase system (IGST) by means of x-ray photoelectron spectroscopy. A systematic shift of Sb 3d and Ge 2p core-level peaks toward lower binding energies side was observed with increasing indium amount, whereas the In 3d and Te 3d core peaks showed less change. The Sb 3d and Ge 2p core-level shift is attributed to an increase in the electronic charge of p-electrons dependent of indium amount. The valence band spectra show a distinct change in the sp configuration with indium concentration change. The change in the local bonding as the indium amount increase has a profound impact on both local atomic arrangement and amorphous-to-crystalline transformation temperature. The difference in the photoemission spectra have been discussed according to a simple structural model suggesting that the Na site in IGST can be occupied by Te, Sb, In, and vacancy, whereas in GST it is occupied only by Te.