During the fast switching in Ge2Sb2Te5 phase change memory devices, both the amorphous and fcc crystalline phases remain metastable beyond the fcc and hexagonal transition temperatures respectively. In this work, the metastable electrical properties together with crystallization times and resistance drift behaviour of GST are studied using a high-speed, device-level characterization technique in the temperature range of 300 K to 675 K.

Resistivity of metastable amorphous Ge 2 Sb 2 Te 5 (GST) measured at device level show an exponential decline with temperature matching with the steady-state thin-film resistivity measured at 858 K (melting temperature). This suggests that the free carrier activation mechanisms form a continuum in a large temperature scale (300 K -858 K) and the metastable amorphous phase can be treated as a super-cooled liquid. The effective activation energy calculated using the resistivity versus temperature data follow a parabolic behavior, with a room temperature value of 333 meV, peaking to ~377 meV at ~465 K and reaching zero at ~930 K, using a reference activation energy of 111 meV (3k B T/2) at melt. Amorphous GST is expected to behave as a p-type semiconductor at T melt ~ 858 K and transitions from the semiconducting-liquid phase to the metallic-liquid phase at ~ 930 K at equilibrium. The simultaneous Seebeck (S) and resistivity versus temperature measurements of amorphous-fcc mixed-phase GST thin-films show linear S-T trends that meet S = 0 at 0 K, consistent with degenerate semiconductors, and the dS/dT and room temperature activation energy show a linear correlation. The single-crystal fcc is calculated to have dS/dT = 0.153 μV/K for an activation energy of zero and a Fermi level 0.16 eV below the valance band edge.

Concentrating Solar Power (CSP) is a promising technology for power generation in which the solar radiation is concentrated to generate high temperature for producing steam in a solar thermal power plant. No fossil fuel is used in this technology; therefore no greenhouse gases are emitted. With an average annual Direct Normal Irradiance (DNI) of 2,000kWh/m 2 the area required to generate 100MWe of electricity is about 2km 2 . Bangladesh receives an average annual DNI of nearly 1,900kWh/m 2 which is sufficient to operate a CSP plant. By the year 2015 the capital cost of CSP plant will become $3,800/kWe. As there is no fuel cost in CSP, this can be an attractive choice to mitigate the power crisis of Bangladesh. In this paper the prospect of utilizing CSP in Bangladesh has been focused.

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