高温動作GaAs系テラヘルツ量子カスケードレーザの研究

背景と現状

Semiconductor THz source has been required because their compact size and high functionality combined with the current integrated circuit. Figure 1 shows the current reported semiconductor THz source.

Figure 1: Current reported semiconductor THz source.

THz QCLs are a promising THz semiconductor light source utilizing carrier recycling and intersubband transition in repeated quantum well structures. The emission wavelength is not limited by the instinct energy band gap of materials.

Figure 2: Schematic of THz QCLs.

現在までの研究

The most important issue limited their widely practical use of THz QCLs is their poor operation temperature. Figure 3 shows the operation temperature and emission frequency of reported THz QCLs. The maximum operation temperature of THz QCLs is 186 K at pulse mode. Our group already successfully realize the Cu-Cu metal-metal waveguide 4-well LO phonon depopulation scheme THz QCLs, which lasing at 3.7 THz and operated to 143 K with few mW output power, which show at the orange point in figure 3.

Figure 3: Operation temperature and emission frequency of reported THz QCLs.

We grow the GaAs based THz QCLs by molecular beam epitaxy (MBE), and using the metal-metal waveguide for optical confinement. The scanning electron microscope (SEM) photograph of the devices shows in figure 4 and following figure 5 is the lasing spectrum with light-output characteristic.

Figure 4: SEM photograph of fabricated THz QCLs.

Figure 5: Lasing spectrum and light-output characteristic THz QCLs.

最近の研究

We use the high-Al-component barriers in AlyGa1-yAs/AlxGa1-xAs THz QCLs, in order to increase the total longitudinal optical (LO) phonon energy in structures. The threshold current density (Jth) reduction with the increasing of Al component has been observed, and consistent with the calculation results at higher operation range. Figure 6 shows the experiment and calculation result of GaAs/ AlxGa1-xAs when x = 0.15 to 0.45.

Figure 6: Experiment and calculation of THz QCLs with different Al component barrier.