Ion beam synthesis of semiconductor nanoclusters in SiO2 films for opto- and microelectronic applications

The contribution will review recent results to the fabrication and investigation of semiconductor nanoclusters (Si, Ge, Sn) embedded in SiO2 films. Due to quantum confinement effects or the large surface/volume ratio of such clusters typical dimensions of only few nanometers exhibit remarkable properties which differ to that of the bulk values. Among different fabrication techniques the ion beam synthesis offers specific advantages to realize a large density of tiny (2-4 nm) nanoclusters and to fulfil the requirements of CMOS technology. The results of presented experiments clearly indicate that the size, density and distribution of clusters are strongly influenced by the implantation and annealing conditions. Taking these influences into account it is possible to realize desired nanocluster distributions in the SiO2 layer, e.g. the fabrication of wide regions with homogeneously distributed clusters or d-like nanocluster bands in thin SiO2 films.
The specific features of semiconductor nanoparticles in SiO2 films comprise an enormous potential for future opto- and microelectronics.
Optoelectronics
In general, group IV nanocluster containing SiO2 films can emit light in a wide wavelength region. The topic of light emission from ion beam synthesized nanoclusters is focused on recent success in extracting intensive violet/blue photo- and electroluminescence (EL) from Si-, Ge- or Sn implanted SiO2 layers which can be attributed to a specific defect formed after the IBS process. A power efficiency up to 0,5 % for EL has been established using MOS structures. Among possible applications the properties of a monolithically integrated optocoupler with ultra low power consumption will be discussed.
Microelectronics
Based on a FET structure with semiconductor nanocluster containing gate oxide, a new non-volatile memory cell has been designed which makes use from the charge storage ability of small quantum dots. The advantages of this memory are attributed to the features, that (i) the nanoclusters act as an ensemble of single storage elements, and (ii) the charge transfer during programming occurs preferably by direct tunnelling. Therefore, lower programming voltages and considerably increased endurance (1010 w/e-cycles) in comparison to the present (Flash)- EEPROM technique is expected. Routes towards the fabrication of a shallow band of nanoclusters in the gate oxide of a FET very close, but well separated to the Si/SiO2-interface will be discussed in detail. CV or IV measurements reveal the charge storage effect of cluster containing thin SiO2 films by a remarkable shift of the flatband or threshold voltage of MOS or FET-structures, respectively. Recently, Zentrum Mikroelektronik Dresden has been successfully realized the first 256 nv-SRAM based on ion beam modified gate oxides.