The Ge2Sb,Tes (GST) thin film is well known to play a critical role in PRAM (Phase Change Random Access Memory). Through device simulation, we found that highresistive GST is indispensable to minimize the writing current of PRAM. For the first time, we tried to increase the GST resistivity by doping nitrogen. Doping nitrogen to GST successfully reduced writing current. Also, the cell endurance

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Ge 2 Sb 2 Te 5 (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.

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The role of hydrogen in the growth of Ge on a Si͑001͒-͑2 3 1͒ surface was studied by scanning tunneling microscopy and medium energy ion scattering spectroscopy. The adsorbed hydrogen was found to (i) increase the number of equilibrium adsorption sites, (ii) lift the diffusion anisotropy, and (iii) lower the diffusivity for Ge adatom, as suggested by the recent first principle calculation. With a dynamically supplied atomic hydrogen flux of ϳ2 monolayers͞s, we achieved layer-by-layer growth by preventing growth of the hut cluster beyond the known critical thickness. The 10.0 monolayer Ge layers grown with hydrogen surfactant are strained, while those without it are relaxed.[S0031-9007(98)06222-X]