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Germanium is one of the most promising materials for high performance infra-red photovoltaic devices. High quality single-crystal germanium on insulator structures can be produced by a Rapid Melt Growth process. Experiments show that thin-film germanium deposited by physical vapor deposition provides better quality in comparison with chemical vapor deposition. The longitudinal optical Ge-Ge peak in Raman spectrum is shifted from the expected 300.2 cm-1 position due to tensile stress resulting from the thermal expansion differences of the materials. The importance of silicon in the rapid melt process is confirmed by the fact that germanium films on sapphire substrates yielded polycrystalline structure. Films produced at high temperature (980 oC) show full width at half maximum values of 3.3 cm-1 indicating good crystalline quality, comparable to bulk germanium (3.2 cm-1). Thus demonstrating the potential to produce low cost high quality germanium films.

Silicon-on-sapphire (SOS) substrates have been proven to offer significant advantages in the integration of passive and active devices in RF circuits. Germanium on insulator technology is a candidate for future higher performance circuits. Thus the advantages of employing a low loss dielectric substrate other than a silicon-dioxide layer on silicon will be even greater. This paper covers the production of germanium on sapphire (GeOS) substrates by wafer bonding. The quality of the germanium back interface is studied and a tungsten self-aligned gate process MOST process has been developed. High low field mobilities of 450-500 cm2/V-s have been achieved for p-channel MOSTs produced on GeOS substrates. Thick germanium on alumina (GOAL) substrates have also been produced.

An atmospheric plasma activation system has been employed to study its application on low temperature wafer bonding. Oxygen activation on PECVD oxide for bonding of temperature sensitive materials shows no pin hole when activating oxide with thickness more than 0.25 microns. Activation on thermal oxide by helium plasma also shows a pin hole free oxide. Bond strength approximately 1000 mJ/m2 is achieved after 250 degree celcius post-bond anneal which is about twice the bond strength of non-activated samples. Multiple UV components from the helium plasma were detected by spectograph. These UV spectra might have contributed to the bond strength enhancement in Si-SiO2 bonding.

Germanium (Ge) has been bonded to fine grain alumina (Al2O3) by means of a polished polycrystalline silicon interface layer. After room temperature bonding and subsequent bond strength annealing at 150 oC for 24 hrs, the germanium layer was ground and polished to 100um. Low temperature Tungsten (W) gate circular geometry devices, W/L = 9, fabricated on this layer exhibited effective mobility values of 150 cm2/Vs. This is much lower than results obtained on equivalent devices on bulk Ge. Improvement in the germanium polish process resulted in transistors with an effective mobility of 415 cm2/Vs, comparable to that of the bulk Ge devices. Low temperature measurement, down to temperatures of 173 K, showed an improvement in device performance resulting in both an increase in effective mobility to 591 cm2/Vs and a decrease in sub threshold slope from 180 mV/dec to 60 mV/dec indicating a reduction in leakage current.

Tungsten gate germanium MOS transistors have been manufactured on bulk germanium platforms. Hole mobility in the range 450 cm2/Vs has been achieved on bulk germanium, but mobility is reduced during the densification of thinner dielectrics at 600C. This may be due to the formation of volatile GeO at the interface during densification. Low temperature measurements of the thinner dielectric device indicate that lattice scattering is dominant at room temperature for the device where the densification was omitted and the excellent subthreshold slopes at low temperatures also indicate devices of good quality.

An atmospheric plasma activation system has been employed to study its application on low temperature wafer bonding. High bond strength (> 2000 mJ/m2) is achieved by oxygen plasma activation on hydrophilic Si-Si and Si-SiO2 bonding at low temperature annealing. This technique has been proved to cause physical damage to thin SiO2 layers (< 0.5 um) creating a high density of pin holes resulting in leaky oxides. When high resistivity substrates are employed the pin holes is reduced by nearly a factor of 7. A germanium disc bonded to plasma treated thin oxide on silicon was electrically connected to the substrate. The atmospheric plasma technique is currently best suited for silicon-silicon bonding, standard SOI, MMIC and MEMS technology.

Al2O3 and HfO2 films were deposited on germanium substrates by atomic layer deposition (ALD) and analyzed by MOS capacitor electrical characterization. In-situ plasma nitridation performed prior to ALD was found to improve the stability of the interface. For Al2O3/GeON/Ge capacitors, a 450degC anneal in nitrogen ambient reduced hysteresis and oxide fixed charge to 90 mV and 1012 cm-2 respectively, with low leakage current density. On the contrary, degradation was observed for un-nitrided Al2O3/Ge capacitors after 300 and 400degC post-metal anneals. HfO2/GeON/Ge capacitors benefitted from a 400degC densification anneal but exhibited degradation after post-metal anneals at temperatures greater than 300degC. This degradation is attributed to the influence of Al electrodes on the HfO2 gate stack. HfO2 is considered to be a suitable material for the gate stack and Al2O3 for the buried dielectric in a GeOI structure.

Hydrogen implantation of germanium is a promising technique for layer transfer. However, both the implantation process, and subsequent heat treatment can create defects in the transferred layer, which detrimentally effect the performance of devices fabricated on these transferred layers. In this study, implanted Germanium wafers were given various anneals and analysed optically and by spreading resistance, to gain insight on the nature of such defects. GeOI layers were produced by thermal splitting of implanted germanium wafers bonded to sapphire handle substrates.

Hydrogen implantation of germanium is a promising technique for layer transfer. However, both the implantation process, and subsequent heat treatment can create defects in the transferred layer, which detrimentally effect the performance of devices fabricated on these transferred layers. In this study, implanted Germanium wafers were given various anneals and analysed optically and by spreading resistance, to gain insight on the nature of such defects. GeOI layers were produced by thermal splitting of implanted germanium wafers bonded to sapphire handle substrates.

An atmospheric plasma activation system has been employed to study its application on low temperature wafer bonding. High bond strength (> 2000 mJ/m2) is achieved by oxygen plasma activation on hydrophilic Si-Si and Si-SiO2 bonding at low temperature annealing. This technique has been proved to cause physical damage to thin SiO2 layers (< 0.5 µm) creating a high density of pin holes resulting in leaky oxides. When high resistivity substrates are employed the pin holes is reduced by nearly a factor of 7. A germanium disc bonded to plasma treated thin oxide on silicon was electrically connected to the substrate. The atmospheric plasma technique is currently best suited for silicon-silicon bonding, standard SOI, MMIC and MEMS technology.

Al2O3and HfO2films were deposited on germanium substrates by atomic layer deposition (ALD) and analyzed by MOS capacitor electrical characterization. In-situ plasma nitridation performed prior to ALD was found to improve the stability of the interface. For Al2O3/GeON/Ge capacitors, a 450°C anneal in nitrogen ambient reduced hysteresis and oxide fixed charge to 90 mV and 1012cm-2respectively, with low leakage current density. On the contrary, degradation was observed for un-nitrided Al2O3/Ge capacitors after 300 and 400°C post-metal anneals. HfO2/GeON/Ge capacitors benefitted from a 400°C densification anneal but exhibited degradation after post-metal anneals at temperatures greater than 300°C. This degradation is attributed to the influence of Al electrodes on the HfO2gate stack. HfO2is considered to be a suitable material for the gate stack and Al2O3for the buried dielectric in a GeOI structure.