Room-temperature electroluminescence at 1.3 and 1.5 μm from Ge/Si quantum-dot light-emitting diodes is reported. The devices were fabricated in a mesa-type structure, with a silicon oxide layer on the top for surface/sidewall passivation. Different passivation processes were employed. We found that the integrated electroluminescence intensities were relatively less sensitive to temperature, persisting at nearly the same intensity up to RT. The fabricated device shows an internal quantum efficiency of about 0.015% at RT. The improved emission property is attributed to the reduced nonradiative recombination centers due to the surface passivation and thermal treatment.

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IntroductionOwing to NAND flash technology facing its scaling limit, resistive random access memory (RRAM) with simple film stack and no cross coupling issue between cells is a promising candidate for future high density memory application [1,2]. The 1TnR architecture with 3D vertical RRAM (VRRAM) structure realizes ultra-low bit cost for high compact density array [3,4]. However, this novel 1TnR structure and processes have not been proved yet. To meet requirements of VRRAM array operation, the nonlinear resistive memory with an excellent self-compliance and low current operation is indispensable [5,6]. A large voltage margin for the device operated with compliance current (ΔV COMP ) and high nonlinearity for the device at low resistance state (LRS) with reliable read voltage should be addressed.In this work, the key processes and the resistive switching for the VRRAM device in the 1TnR architecture are firstly demonstrated. Moreover, the TaO X /HfO X (TH) device with 1 μA operation current exhibits a large ΔV COMP (~ 1.6 V) for reliable pulse mode operation. Besides, a high LRS nonlinearity ~ 40, which can provide enough read/write margins in the VRRAM array for robust operation, is extracted from the reliable read voltage based on the constant voltage stress (CVS) test.VRRAM in 1TnR architecture Figure 1 shows the key process flow for the VRRAM device in the 1TnR architecture. Firstly, the via hole of oxide/metal multilayers were defined and etched to form the horizontal electrodes (HE) with a thickness of 40 nm, as shown in Fig. 1(a). Then, the Ta and HfO X films, respectively grown with PVD and ALD methods, and a thin TiN protection metal layer were conformally deposited, as depicted in Fig. 1(b). To open the connected hole above the bottom access transistor, the etch-back process was adopt to remove the Ta/HfO X film above the transistor via, as shown in Fig. 1(c). The HfO X VRRAM devices can keep damage-free by the protection of TiN layer during the etch-back process. Finally, as presented in Fig.1 (d), the vertical electrode (VE) was formed by the TiN metal filling the hole with the subsequent CVD process. Figure 2 demonstrates the cross-section TEM image of four VRRAM devices within the 1TnR architecture.In Fig. 3, it shows the distributions of forming voltage (V F ) for the HfO X VRRAM. Also, there is no obvious difference for the V F of the top and bottom vertical devices. The V F is larger than 5V due to small area HE (~0.018 μm 2 ), which fits well with the dependence of V F for the Ta/HfO X device on the cell size based on oxide breakdown theory [7], as shown in the inset of Fig. 3. These results prove the process stability for the initial behavior of VRRAM devices during forming in the 1TnR architecture. As shown in Fig. 4, the HfO X VRRAM device exhibits the robust resistive switching behavior with the on/off ratio larger than 10.

Pretreatment of silicon surface with SiCH 6 was used to modify the Stranski-Krastanow growth mode of Ge on Si͑001͒ at 550 °C by ultrahigh vacuum chemical vapor deposition. With the appropriate SiCH 6 mediation, the elongated Ge hut clusters can be transformed to highly uniform multifaceted domes with a high Ge composition at the core. These SiCH 6 -mediated Ge dots have an average diameter and height of 38 and 7 nm, respectively. The modified growth mode for the formation of SiCH 6 -mediated Ge dots can be attributed to ͑i͒ an almost hydrogen-passivated Si surface to limit the nucleation sites for dot formation and ͑ii͒ the incorporation of Ge atoms, repelled by the C-rich areas, into the existing Ge dots. The results also demonstrate that SiCH 6 -mediated dots exhibit the improved field emission characteristics compared to shallow Ge huts.

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