Aug 24, 2015

Integration techniques of pHEMTs and planar Gunn diodes on GaAs substrates

This work presents two different approaches for the implementation of pseudomorphic high electron mobility transistors (pHEMTs) and planar Gunn diodes on the same gallium arsenide substrate. In the first approach, a combined wafer is used where a buffer layer separates the active layers of the two devices. A second approach was also examined using a single wafer where the AlGaAs/InGaAs/GaAs heterostructures were designed for the realisation of pHEMTs. The comparison between the two techniques showed that the devices fabricated on the single pHEMT wafer presented superior performance over the combined wafer technique. The DC and small-signal characteristics of the pHEMTs on the single wafer were enhanced after the use of T-gates with 70 nm length. The maximum transconductance of the transistors was equal to 780 mS/mm with 200 GHz maximum frequency of oscillation (fmax). Planar Gunn diodes fabricated in the pHEMT wafer, with 1.3 μm anode-to-cathode separation (LAC) presented oscillations at 87.6 GHz with maximum power of oscillation equal to −40 dBm.


Aug 7, 2015

GaAs solar cell on Si substrate with good ohmic GaAs/Si interface by direct wafer bonding


We report wafer bonding (WB) techniques giving good ohmic interfaces of GaAs/Si.
WB with a low bonding temperature and short processing time was performed.
We demonstrated the GaAs solar cell on Si substrate by WB techniques.
Fabricated GaAs solar cell on Si exhibited a comparable performance with that on GaAs.
We proved the feasibility of stable WB technologies of GaAs/Si substrates.


In this work, we developed wafer bonding techniques to bond GaAs and Si wafers. Wafer bonding was carried out at room temperature without high temperature annealing processes. The bonded interface showed a low interface resistance of 8.8×10−3 Ω cm2. We also exploited the new bonding techniques to fabricate a GaAs solar cell on a Si substrate. The solar cell showed a high energy conversion efficiency (13.25%) even without an anti reflection coating. The performance of the fabricated GaAs/Si solar cell was comparable to that of a homogeneous GaAs solar cell grown on a GaAs substrate. *Corresponding author.