Optoelectrical Operation Stability of Broadband PureGaB Ge-on-Si Photodiodes with Anomalous Al-Mediated Sidewall Contacting

An anomalous aluminum-mediated material transport process was investigated in sets of Ge-on-Si photodiodes with broadband optoelectrical characteristics measured at wavelengths from 255 nm to 1550 nm. The diodes had “PureGaB” anode regions fabricated by depositing a Ga wetting layer capped with an 11-nm-thick B-layer on 0.5 µm-thick Ge islands grown on Si. The Al metallization was able to reach the Ge-Si interface through ~ 0.1-µm-wide holes inadvertently etched along the perimeter of the Ge-islands, and then traveled along the Ge-Si interface, displacing and recrystallizing Ge and Si. The rest of the Ge surface was protected from the Al contact metallization by the B-layer. For diodes that had received the standard 400°C Al alloying step, the responsivity was near-theoretical at 406 nm and 670 nm, but, at 1310 nm and 1550 nm, the proximity of Ge-Si interfacial defects caused significant attenuation. Extra annealing at 400°C or 500°C enhanced the formation of Si pits that were filled with modified Ge crystals alloyed with Si and p-doped with Al. All these diodes maintained low dark currents, below 50 µA/cm2 at 2 V reverse bias, but the responsivity was degraded, particularly for the long wavelengths. On the other hand, neither responsivity nor degradation of current–voltage (I–V) characteristics was observed for prolonged exposure to normal operating temperatures up to 100°C. Since the direct Al contacting of the Ge sidewalls does not degrade the dark current, for large diodes it could be a low-cost method of obtaining low contact resistance to an anode with p-type sidewall passivation and high fill-factor.

GE SiC Semiconductor Device Operation at Extreme Temperatures

GE Research has been working on the design, packaging, and testing of SiC Power semiconductors devices at junction temperatures up to 500°C for the past 5 years. Intrinsically, SiC power devices are able to endure and operate reliably at harsh environments. Limiting factors to packaged devices’ operation at high temperature are the contact metallization and packaging. While testing bare die power devices, probe contact resistance was found to be an issue for resistance measurements at very high temperatures. On the backside contact, traditional die attach solders have operational temperature limits. Using insulated metal substrates, sintered die attach, and wedge bond interconnect, GE Research tested its power devices up to 500°C junction temperature. GE Research also demonstrated various junction termination dielectric stackups which can block up to 1000V at 500°C junction and show improvements over traditional organic dielectric options (e.g. Epoxy, Silicone, Polyimide).

Investigation of the Screen-printable Ag/Cu Contact for Si Solar Cells Using Microstructural, Optical and Electrical Analyses

ABSTRACTIn a bid to further reduce the cost of the front Ag contact metallization in Si solar cells, Cu is the potential alternative to replace the Ag in the Ag paste. However, this requires an understanding of the contact mechanism of screen-printable Ag/Cu paste in Si solar cell through rapid thermal process. The pastes with different weight percent of Cu (0 wt%, 25 wt% and 50 wt%) were used and the Voc of the cells was reduced with the increasing weight percent of Cu. This is because the presence of Cu in the paste changed the microstructure of the Ag/Cu/Si contact through Cu doping of the glass frits and hence increasing the Tg of the glass. The increased Tg of the glass impeded the uniform spreading of the molten glass and resulted in poor wetting and etching of the SiNx, which impacted the contact as evident in ideality factor of less than unity. This also led to the formation of agglomerated Ag crystallites with features of 700 nm in length and 200 nm in depth, which is close to the p-n junction, of which depth is ∼300 nm. However, the interface glass layer acted as an effective diffusion barrier layer to prevent Cu atoms from diffusing into the Si emitter, which is quite remarkable for Cu not to diffuse into silicon at high temperature. Further investigation of the Ag/Cu contacts with the conductive AFM in conjunction with the SEM and STEM analyses revealed that the growth of Ag crystallites in the Si emitter is responsible for carrier conduction the gridlines as with the pure Ag paste.

Effectiveness of Sensors Contact Metallization (Ti, Au, and Ru) and Biofunctionalization for Escherichia coli Detection

In designing a bacteria biosensor, various issues must be addressed: the specificity of bacteria recognition, the immobilization of biomolecules that act as the bacteria receptor, and the selectivity of sensor surface. The aim of this paper was to examine how the biofunctionalized surface of Ti, Au, and Ru metals reacts in contact with strains of Escherichia coli (E. coli). The focus on metal surfaces results from their future use as electrodes in high frequency biosensors, e.g., resonant circuits or transmission-line sections. First, the surfaces of different metals were chemically functionalized with 3-aminopropyltriethoxysilane (APTES) and glutaraldehyde or with 3-glycidylooxypropyltrimethoxysilane (GPTMS) followed by N-(5-amino-1-carboxypentyl) iminodiacetic acid (AB-NTA) and NiCl2. Secondly, the lipopolysaccharide binding protein (LBP), polyclonal anti-Escherichia coli antibody and bacteriophage protein gp37 were tested as bacteria receptors. The selectivity and specificity have been confirmed by the Enzyme-Linked Immunosorbent Assay (ELISA) and visualized by scanning electron microscopy at low landing energies. We noticed that LBP, polyclonal antibody, and gp37 were successfully immobilized on all studied metals and recognized the E. coli bacteria selectively. However, for the antibody, the highest reactivity was observed when Ti surface was modified, whereas the bacteria binding was comparable between LBP and gp37 on the functionalized Ru surfaces, independent from modification. Thus, all surfaces were biocompatible within the scope of biosensor functionality, with titanium functionalization showing the best performance.