Wafer Bonding Of Si-based Semiconductor Materials Based On Amorphous Transition Layer And Study Of Wafer-bonded Ge/Si Near-Infrared Photodetectors

Due to the lattice mismatch and the thermal mismatch between Ge and Si,the threading dislocation density(TDD)in the Si-based Ge film is still too high.In recent years,the investigation of low-temperature Ge/Si wafer bonding provides potential methods for further decreasing the TDD in the Ge film.The Ge/Si wafer bonding can be achieved at low temperature of 300?.The nucleation and diffusion of the TDs are limited at low temperature.The TDD is very low in bonded Ge film.More importantly,the quality and photoelectric characteristic of the bonded Ge film can be comparable with the bulk Ge.Thus,low-temperature Ge/Si wafer bonding is a potential method for the fabrieation of high-quality Si-based Ge film.However,the study of Ge/Si wafer bonding is still not enough,lots of bubbles appear at Ge/Si bonded interface when the wafers are contacted in the atmosphere.In addition,a 2-3 nm thick oxide layer appears at the Ge/Si bonded interface due to the hydrophilic reaction(like Si/Si wafer bonding).Thus,the carrier migration at the bonded interface is limited and the device performance may deteriorate.In this thesis,we innovatively introduce an amorphous transition layer at Ge/Si bonded interface to achieve wafer bonding.How to achieve the exfoliation of Si-based Ge layer at low temperature and decrease the dark current density of the Ge/Si p-i-n photodiode are investigated.Finally,the theoretical analysis of the single-photon characteristics of wafer-bonded Ge/Si single-photon avalanche photodiode is carried out.The detail works and results are as follow.1,The effect of sputtering condition of magnetron sputtering system on the root-mean-square(RMS)and hydrophilia of the amorphous Ge(a-Ge)layer is investigated.The extremely flat and hydrophilic a-Ge thin film is obtained.The a-Ge transition layer is used to achieve near-bubble-free and oxide-layer-free Si/Si and Ge/Si wafer bonding with high bonding strength at low temperature.The a-Ge at Si/Si boned interface becomes poly crystalline Ge(poly-Ge)after bonding.While the a-Ge at Ge/Si bonded interface becomes single-crystal Ge(c-Ge)after bonding.Serious atom migration occurs at the bonded interface due to the crystallization of a-Ge,leading to the decomposition of oxide layer.We also investigate the effect of annealing temperature and a-Ge layer thickness on the bubbles at Si/Si bonded interface.With the increase of the annealing temperature and a-Ge layer thickness(400?),the bubble density decreases,leading to the increase of the bonding strength.The a-Ge in the bubbles starts to crystallize from the center of the bubbles and extends to the bubble edge,leading to the disappearanee of the bubbles.We also study the effect of bonded eonditions on the bubble density at Ge/Si bonded interface.With the decrease of the exposure time,the bubble density at Ge/Si bonded interface decreases gradually.A near-bubble-free bonded interface is achieved when the exposure time of 3 s is applied.2.We use chemical corrosion and CMP technique to polish the Ge film(FWHM of XRI peak of the Ge film=34")and achieve the fabrication of Ge/Si heterojunction diode.The on/off ratio of 3.4X105,the ideality factor of 1.75 at 300 K,and the responsivity of 0.61 A/W at 1310 nm and that of 0.24 A/W at 1550 nm of the Ge/Si heterojunction diode is achieved.In addition,due to the 0.205%tensile strain in the Ge film,the responsivity of 94 mA/W at 1630 nm can be achieved.This indicates that the wafer-bonded Ge/Si diode is suitable for the optical communication in all WDM band.3.We achieve the exfoliation of Si-based Ge film using Ge/Si wafer bonding and Smart-Cut technique.The FWHM of the XRD of the Ge film is 96"(1 ?m),which is much smaller than that of epitaxial Ge film.The point defects in the Ge film have been repaired and the compressive strain in the Ge film turns into tensile strain after post-annealing at 500? for lh.However,the TDD in the Ge film increases after post-annealing.We fabricate a Ge/Si p-i-n photodiode at a low temperature of 300? by Ge layer exfoliation and laser annealing.The low dark current density of 5.97 mA/cm2 of the p-i-n photodiode is achieved.This value is lower than that of epitaxial p-i-n photodiode and the ideality factor of 1.19 is achieved at 300 K.After post-annealing at 500?,the tensile strain appears in the Ge film,leading to the decrease of the Ge bandgap and the increase of the light absorption in infrared range.Finally,the responsivity of 0.71 A/W at 1310 nm and that of 0.524 A/W at 1550 nm are achieved for wafer-bonded Ge/Si p-i-n photodiode.4.We investigate the performance of wafer-bonded Ge/Si single-photon avalanche photodiode by Silvaco and Matlab software.The effect of oxide layer thickness and the interface state density at Ge/Si bonded interface on the device performance is investigated.In addition,the effect of interface state density at Si/Si bonded interface fabricated hydrophobic wafer bonding and high-vacuum wafer bonding on the performance of the device is also studied.The thick interface oxide and the high interface state density significantly worsen the device performance.On the other hand,the study of the effect of the pulse repetition rate on the performance of the epitaxial and wafer-bonded Ge/Si single-photon avalanche photodiode is carried out.The pulse repetition rate of 28 MHz is achieved for wafer-bonded device,which is much higher than that of the epitaxial one(4-8 MHz).In addition,the wafer-bonded device can be operated at near-room temperature due to the extremely low dark current.