Desigh And Fabrication Of GaN-based Lasers With An Inverted Ridge Waveguide

Due to the issues of large series resistance and high thermal resistance,the operating junction temperature of conventional GaN-based laser diodes(pRW-LDs)is relatively high,which seriously affects the performance of the device.To circumvent these issues,an innovative LD structure is proposed to develop GaN-based LDs with an n-side ridge waveguide(nRW-LDs)that is fully compatible with the Si-based CMOS platform and can be utilized in monolithically integrated Si photonics.We have investigated the key issues about nRW-LDs including structure design,material growth,device fabrication,and characterization.The results are as follows.1.An innovative LD structure-nRW-LDs is proposed,of which the ridge structure is inverted from p-side to n-side.The nRW-LDs are blanketed with p-electrode,resulting in a substantially larger hole injection area.This greatly reduces the device resistance,thereby slashing the operation voltage and Joule heat.Moreover,nRW-LDs are p-side down bonded to the heatsink at the wafer level,which effectively shortens the heat dissipation path and cuts the thermal resistance.The reduction in both thermal resistance and Joule heat generation can effectively cool down the laser junction and hence improve the wall-plug efficiency and the reliability of the LDs.2.The structure of nRW-LDs was carefully designed.After optical simulation design,the optica sumulation result showed that optical confinement factor of the active region can be improved by 10.5%,and the internal loss is reduced by 21%.We establied the resistance analysis model applied to nRW-LDs and proved the current spreading effect in nRW-LDs by simulation calculation.In response this issue,we propose an experimental plan to suppress the current spread effect by mudilating doping.The results show that the current spreading effect is effectively suppressed.3.We have developed the complete device fabrication for nRW-LD.The effect of surface stoichiometry on the ohmic contact to N-face n-GaN was investigated combined with XPS surface testing.As a result,a non-alloyed ohmic contact to N-face n-GaN can be obtained reproducibly with a specific contact resistivity on the order of low 2.5×10-4 ?·cm2,which remains stable even after rapid thermal annealing at a temperature below 350?.A F-P facet preparation method combining ICP dry etching and FIB was developed,and the facet with a flat surface,small etching damage and verticality was obtained.4.A nRW-LDs on exact Si(100)has been demonstrated under room-temperature continuous-wave current injection,which is fully compatible with CMOS industry.The threshold current is 350 mA,which corresponds to a threshold current density of 4.3 kA/cm2.The I-V test shows that the differential resistance of the nRW-LDs(at 350 mA)is only 52%of the pRW-LDs.And the working voltage is effectively reduced by 1.41 V.The forward voltage method and the threshold current method were used to test the thermal resistance of nRW-LDs.It can be confirmed that the thermal resistance and junction temperature of nRW-LDs were reduced by 8 K/W and 25?,respectively.The thermal resistance model of was established,and the simulation results indicated that it can be further reduced by twenty-eight percents when the high thermal conductivity Cu solder is used.