Heterogeneous integration of transfer bonded terahertz quantum cascade lasers for improved heat management and light coupling

Terahertz quantum cascade lasers (THz QCLs) in metal-metal (MM) ridge waveguides have been fabricated and hetero bonded on aluminum nitride (AlN) substrate as heat sink submount. Compared with the conventional structure of THz QCLs in MM waveguides on gallium arsenide (GaAs) as receptor substrate, AlN performs superior heat dissipation properties for thermal management due to its much higher thermal conductivity. The light–current density–voltage (L-J-V) characterization shows comparable maximum operating temperature (Tmax) at 93-95 K for both THz QCLs bonded on AlN and GaAs under short pulse injection (250 ns). However, as the injected pulse duration increases for THz QCLs on GaAs, the light intensity drops quickly, eventually leading to lasing quenching when the pulse duration is above 30 µs at 80 K (heat sink temperature). On the other hand, THz QCL on AlN shows much stronger light intensity and slower decrease with the increase of the pulse duration; for example, the light intensity is 100 times higher for the THz QCL on AlN (pulse duration of 40 µs) than THz QCL on GaAs (pulse duration of 30 µs) at the same measurement conditions at 80 K. This study shows suspected joule heating plays a great role on THz QCLs operating from long duty cycle towards continuous-wave (CW) mode, indicating AlN substrate as a high thermal conductivity material produces superior thermal management for heat extraction and dissipation.