Gigahertz modulation of GaAs-based bipolar cascade vertical cavity surface-emitting lasers

Area of Science:

• Optoelectronics
• Semiconductor Lasers
• Materials Science

Background:

• Vertical cavity surface-emitting lasers (VCSELs) are crucial for high-speed optical communication.
• Gallium arsenide (GaAs)-based VCSELs offer potential for high-frequency operation.
• Cascade structures and tunnel junctions can enhance device performance.

Purpose of the Study:

• To investigate the high-frequency modulation characteristics of GaAs-based bipolar cascade VCSELs.
• To evaluate the impact of device architecture (two-stage vs. three-stage) on modulation performance.
• To determine the operational limits of these lasers at cryogenic temperatures.

Main Methods:

• Fabrication of GaAs-based bipolar cascade VCSELs with specific heterostructures.
• Utilized p-doped Al0.98Ga0.02As oxide apertures and GaAs tunnel junctions.
• Performed small-signal current injection measurements to assess modulation response.
• Conducted measurements at a low operating temperature of -50 degrees C.

Main Results:

• Measured -3 dB modulation bandwidths for the VCSELs.
• Achieved a modulation bandwidth of 6.5 GHz for two-stage devices.
• Achieved a higher modulation bandwidth of 9.4 GHz for three-stage devices.
• Demonstrated stable operation at -50 degrees C.

Conclusions:

• GaAs-based bipolar cascade VCSELs exhibit significant high-frequency modulation capabilities.
• Three-stage devices show superior modulation performance compared to two-stage devices.
• These lasers are promising for high-speed optoelectronic applications, especially at reduced temperatures.