Investigation Of GaN Based Light-emitting Diodes Electrical Characteristics And Nanscale Optoelectronic Device

For the direct band gap covers a wide spectrum range from infrared to ultraviolet(from 0.7eV to 6.2eV),?-nitride semiconductors are the most favorite material system for solid-state lighting device applications.Through two decade years'investigation,?-nitride material and conventional light-emitting diodes(LEDs)and lasing diode(LDs)have been greatly developed.Recently,the realization of transformative application including miniaturized smart display,super-resolution and sophisticated biomedical imaging in the integrated photoelectric device,it is crucial to develop efficient and compact ?-nitride nanoscale diodes.In the dissertation,it discusses temperature dependent current-voltage(T-I-V)properties from the planar GaN-based blue and green LEDs,investigates the carriers transport mechanism.After that,InGaN/GaN single nanorod(NR)LEDs have been successfully fabricated through reducing the size of the device,and obtained the submicron illumination source with high polarization degree.GaN-based plasmonic nanolaser with low optical pumping power density has been demonstrated using surface plasmon amplification of stimulated emission of radiation.The main conclusions are listed as follows:1.A UV-photolithography,physical vapor deposition(PVD)and lift-off process were employed to form planar GaN-based LEDs(?300 ?m*300 ?m).Through investigating the temperature dependent current-voltage(T-I-V)properties of GaN based blue and green LEDs in this study,it is proposed an asymmetric tunneling model to understand the leakage current below turn-on voltage(V<3.2 V):At the forward bias within 1.5 V?2.1 V(region 1),the leakage current is main attributed to electrons tunneling from the conduction band of n-type GaN layer to the valence band of p-type GaN layer via defect states in space-charge region(SCR);While,at the forward bias within 2 V?2.4 V(region 2),heavy holes tunneling gradually becomes dominant at low temperature(T<200K)as long as they can overcome the energy barrier height.This asymmetric tunneling model shows a novel carrier transport process,which provides better understanding of the leakage characteristics and is vital for future device improvements.Three domains of reverse leakage current dependence were verified,and different charge carrier transport mechanisms for each domain were discussed:the variable-range hopping(VRH)conduction(T<250K)and Poole-Frenkel emission(T>250K)are responsible under the low reverse bias(V<12V).As the external bias increasing(V>12V),the reverse leakage current is dominated by space-charge-limited conduction mechanism gradually.2.After investigated plane GaN based LEDs,GaN based LEDs with array nanorods structure have been fabricated by utilization of nanoimprint lithography(NIL).It demonstrates the uniform and bight emission,lower leakage current(?10-7),optimized turn on voltage(-3V).It is confirmed that strain accumulated in the film was released,quantum-confined Stark effect was reduced,the wave function overlap of electron and holes was increased and light extraction efficiency was improved.3.InGaN/GaN single nanorod(NR)LED has been successfully fabricated by NIL and focused ion beam induced deposition.The current-voltage characteristics of single NR LEDs show low leakage current of 2×10-12 A at a reverse bias of-5 V and turn-on voltage of?3.8 V.Linear polarization oriented parallel to the c-axis with a degree of-50%was discovered from the electroluminescence(EL)emission of a single NR LED.Such nano-sized polarized EL sources might give birth to new applications for optoelectronic integration.4.GaN/InGaN based plasmonic nanolaser has been demonstrated using hybrid metal-oxide-semiconductor(MOS)structure,consisting of a semiconductor nanorod separated from a noble metal surface by a dielectric gap.Elliptic nanorods were intentionally designed and fabricated for both single and multi-modes nano-lasing with low optical pumping power density of 1.5 kW/cm2,where the full width half maximum(FWHM)of emission peak at the wavelength of 490 nm dramatically declined to 5 nm.The quality factor(Q factor)reaches up to 123,and the ? factor has been obtained to be 0.48.Through finite-different time-domain(FDTD)and MODE solutions simulations,not only the surface plasmon polariton(SPP)coupling induced strong electric field confinement in MOS structure has been confirmed,but also the association between elliptic nanorod morphology and lasing modes has been found and discussed.The hybridization of plasmonic and photonic modes is the key to manipulate lasing modes,which have been experimentally confirmed and might give innovative insight to fulfill luminescence device.