Studies of Light Emitting Devices Based on Er-doped Si and SiGe Layered Structures

Abstract: Doping with rare earth element erbium (Er) in Si has recently attracted a lot of research interest due to potential applications in Si-based opto-electronics. By using molecular beam epitaxy (MBE), precipitate-free Er-doping in Si has been made together with other co-dopants, e.g., oxygen (0) and fluorine (F), up to a level ∼1020 cm-3. Together with other capabilities of high quality growth of layered structures with desired doping profiles and heterojunctions offered by MBE, several types of dedicated Er-doped Si and Si/SiGe light emitting devices have been designed, processed, and characterized, aiming at finding a possible solution for efficient Sibased light emitters.During the thesis work, mainly three types of Er-doped Si light emitting devices: Schottky-type light emitting diode (LED), p-i-n LED, and heterojunction bipolar transistor (HBT), have been studied for light emission from either the surface or an edge. Three kinds of Er-containing sources, namely Er2O3 , ErF3 , and elementa lEr together with SiO were used for doping. In order to get comparative results from electroluminescence (EL) and photoluminescence (PL) measurements using the same sample, Schottky-type LEDs using Er/O structures were fabricated and characterized, where Er3+ ions can be excited using an impact process of hot electrons generated in the depletion region at reverse bias. A number of grown Si:Er:O and Si:Er:F p-i-n structures were processed into LEDs, and EL from these devices was studied both at forward bias and reverse bias conditions. The light emission from forward biased p-i-n diodes was concluded to be due to the carrier-recombination-mediated energy transfer process, however, luminescence could not persist to room temperature (RT) due to the strong quenching process induced by the energy back transfer process and other nonradiative processes. For reverse biased p-i-n diodes, especially for the structure designed favoring the electron tunneling, intense EL was observed via direct carrier impact excitation process, which persisted up to RT or even higher. In order to have independent control over the injection current and the applied bias, and de-couple their influence on the EL intensity, Si/SiGe/Si:Er:O-HBTs with Er3+ ions incorporated in the collector have been fabricated with layered structures prepared by differential MBE growth. Careful EL studies have been carried out by operating an HBT in a linear regime prior to the avalanche breakdown. The effective Er impact cross-section has shown a 100-fold increase compared with conventional Si:Er-LEDs. The temperature dependent EL measurements on different types of devices have indicated that an Er-induced defect level located at 150 meV below the conduction band is mainly responsible for thermal quenching of the luminescence intensity, which is the same value as obtained in PL measurements. Time-resolved EL measurements have exhibited that Auger-carrier de-excitation plays an important role in reducing EL intensity. Moreover, it has revealed that not only ionized equilibrium carriers but also injected excess carriers act as Auger de-excitation centers. Finally, the results of the thesis work suggest that if the HBT structure can be combined with a high optical activation of Er3+ ions, an efficient Si-based light emitter is possible.