Theoretical investigation of metal-cavity nanolasers and nanoLEDs and comparison with experiments

Nanolasers;nanoLEDS;high-speed modulation;Thermal effect;Light-emitting diode (LED)

Ni, Chi-Yu

关键词: Nanolasers;    nanoLEDS;    high-speed modulation;    Thermal effect;    Light-emitting diode (LED);   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/31032/NI_CHIYU.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Using metal to confine light in a small cavity and to make a light-emitting devicehas been intensively investigated recently since it provides a new approach to reducethe size of light-emitting devices. In the presence of metal, the optical mode volumeof either a dielectric mode or a plasmonic mode can be suppressed to be smaller thanits counterpart in conventional dielectric cavities. Furthermore, the mode volume of theplasmonic mode can be smaller than the diffraction limit, which is the volume with halfa wavelength in three dimensions, due to the nature of the surface wave. Many groupshave shown experimental work on metal cavity lasers. To understand the metal effecton metal-insulator-semiconductor-insulator-metal (MISIM) slab and circular waveguides,we derive their guiding conditions. The analysis gives us the intuition on metal cavitylaser design. For the non-circular cross section of a nanodisk such as ZnO, which has ahexagonal cross section, the resonant modes in different metal cavities will be calculatedwith the finite-difference time-domain method (FDTD). Our investigation shows theenhancement of metal on the optical field confinement and the reduction of the radiationloss from metal. The threshold material gain can be improved by one third comparedwith that of the same cavity without metal encapsulation.On the other hand, due to the dispersive characteristics of metal, we use a rigorousformula for electromagnetic energy in dispersive material and the positive energy is alwaysobtained whatever the operating frequency. We then apply Poynting’s theorem to calculate the quality factor (Q) of a nanobowtie antenna and further analyze its radiationpattern and material loss. The calculated Q agrees well with the experimental data and,thus, the validity of the formula is verified.The third study is to analyze the metal-cavity surface-emitting lasers, fabricated byour group. The metal-cavity microlasers show the highest power among current metalcavitylasers and they operate at continuous-wave (CW) electrical injection at roomtemperature. We study this structure from calculating its gain profile of coupled multiplequantum wells (MQWs) and fit the experimental light output power versus the current(L-I) curve using the rigorous rate equations with temperature dependence. Our studyshows that the nonradiative recombinations, including the surface recombination andAuger recombination, dominate the threshold current.The high-speed modulation response of metal-cavity light-emitting devices is theninvestigated. Since the spontaneous emission plays an important role in a small cavity,especially when it works in the LED region, we derive the complete representation forthe spontaneous emission in a metal cavity and show that the Purcell effect appearsnaturally in the spontaneous emission formula, instead of being artificially placed inthe spontaneous emission rate in free space. We show the dependence of the maximumbandwidth on the quality factor Q and the normalized effective optical modal volume Vn,for bulk, multiple quantum wells, and quantum dots, using our rigorous rate equations.The effects of the optical mode volume, the quality factor, and the active materials arethoroughly discussed.Finally, to realize a small metal-cavity laser, the potential design rules are presented.