PL Spectra and Hot Charge Carrier Phenomena in an Undoped GaAs/AlGaAs Tunnel-Coupled Quantum Well

In this research, we experimentally investigated the photoluminescence (PL) spectra of an undoped GaAs/Al0.36Ga0.64As Tunnel-Coupled Quantum Well (TCQW) at 300 K and 77 K. At 300 K, PL spectra were broadened at various laser intensities due to the characteristic quantum-confinement electron levels in the active region of the TCQW during pumping excitation. At 77 K, at selected excitation intensities, the high-energy tails in the PL spectra of the studied structure corresponded with hot electron temperatures as functions of the energy of emitted photons. The average scattering energy rate of hot electrons in the system was also studied at a lattice temperature of 77 K. The average scattering energy rate of hot electrons obtained from this experimental study was in agreement with the calculated theoretical value.

Asymmetric Ge/SiGe coupled quantum well modulators

We design and demonstrate an asymmetric Ge/SiGe coupled quantum well (CQW) waveguide modulator for both intensity and phase modulation with a low bias voltage in silicon photonic integration. The asymmetric CQWs consisting of two quantum wells with different widths are employed as the active region to enhance the electro-optical characteristics of the device by controlling the coupling of the wave functions. The fabricated device can realize 5 dB extinction ratio at 1446 nm and 1.4 × 10−3 electrorefractive index variation at 1530 nm with the associated modulation efficiency V π L π of 0.055 V cm under 1 V reverse bias. The 3 dB bandwidth for high frequency response is 27 GHz under 1 V bias and the energy consumption per bit is less than 100 fJ/bit. The proposed device offers a pathway towards a low voltage, low energy consumption, high speed and compact modulator for silicon photonic integrated devices, as well as opens possibilities for achieving advanced modulation format in a more compact and simple frame.

Controlled electron leakage in electron blocking layer free InGaN/GaN nanowire light-emitting diodes

In this study, we have proposed and investigated the effect of coupled quantum wells to reduce electron overflow in InGaN/GaN nanowire white color light-emitting diodes. The coupled quantum well before the active region could decrease the thermal velocity, which leads to a reduced electron mean free path. This improves the electron confinement in the active region and mitigates electron overflow in the devices. In addition, coupled quantum well after the active region utilizes the leaked electrons from the active region and contributes to the white light emission. Therefore, the output power and external quantum efficiency of the proposed nanowire LEDs are improved. Moreover, the efficiency droop was negligible up to 900 mA injection current.