Amorphous-to-crystal transition of nitrogen- and oxygen-doped Ge2Sb2Te5 films studied by in situ resistance measurements

Abstract

The amorphous-to-crystal transition has been studied through in situ resistance measurements in Ge2Sb2Te5 thin films doped by ion implantation with nitrogen or oxygen. The dependence of the electrical resistivity and structure on the annealing temperature and time has been investigated in samples with different dopant concentrations. Enhancement of the thermal stability and increase of the mobility gap for conduction have been observed in O- and N-doped amorphous Ge2Sb2Te5. Larger effects have been found in the case of nitrogen doping.

Study on the crystallization by an electrical resistance measurement in Ge2Sb2Te5 and N-doped Ge2Sb2Te5 films

“…The higher temperature used for N-GST is due to increasing of the crystallization temperature for GST after N doping. 7,16,17 RESULT AND DISCUSSION Figure 1 shows the resistance as a function of time measured at 140°C in an undoped GST film. The as-deposited sample was amorphous.…”

“…It indicated that N-GST was also crystallized layer by layer and it is in agreement with observation on ion-implanted N-doped sample. 16 By resistance measurement and an analysis procedure similar to GST, we also got the JMAK parameters of N-GST. Figure 4 is the result of the sample annealed at 165°C and the plot of ln͑−ln͕͑ c − ͒ / ͓ c − ͑ ͔͖͒͒ as a function of ln͑tЈ͒ is a straight line with slope of 1.59 ͓Fig.…”

“…The pure Ge 2 Sb 2 Te 5 ͑GST͒ and nitrogendoped Ge 2 Sb 2 Te 5 ͑N-GST͒ were investigated, which can enhance the cell endurance and reduce the writing current for PCRAM than GST. 7,16,17 Then, the results for the GST and the N-GST have been compared to obtain how the nitrogen doping affects the crystallization parameter of GST.…”

“…1-4 The resistivity measurement was also used to get information about the crystallization processes. 6,9,16,17 The crystallization temperature and the effective activation energy of GeSbTe were obtained through this method. However, for PCRAM, there are still some problems.…”

“…Therefore, a considerable number of studies for the kinetics of amorphous-crystalline transformation in phase-change media have been done. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Oshima, 1 Jeong et al, 2 Weidenhof et al, 3 Ruitenberg et al, 4 and Laine et al,5 reported that the crystallization behaviors of the GeSbTe films in isothermal condition satisfy the Johnson-Mehl-Avrami-Kolmogrov ͑JMAK͒ equation f =1 − exp͑−kt n ͒, where f is crystallinity, n is the Avrami coefficient, and k is an effective rate constant describing both the nucleation and growth. The JMAK parameters such as Avrami coefficient, activation energy, etc.…”