Electrical, optical, and morphological studies of quantum confined InAs and GaAs semiconductor nanoparticles

Extensive electrical optical, and morphological studies of InAs and GaAs semiconductor nanocrystallites (Q-InAs and Q-GaAs) are reported. Morphological studies employed scanning tunneling microscopy (STM) and atomic force microscopy (AFM) imaging to determine the size distributions of Q-InAs and Q-GaAs deposited onto Au and Pt surfaces. STM and AFM studies of films of Q-InAs, and of single Q-InAs particles, and STM imaging of films of Q-GaAs revealed particles' sizes well below the corresponding Wannier exciton diameters for these materials.; Electrical studies included the use of tunneling spectroscopy (TS), macroscopic I-V measurements on interdigitated array (IDA) electrodes, and electrochemical measurements in solution. TS I-V plots under a nonconductive fluid of Q-InAs films on Au revealed a HOMO-LUMO energy gap wider than the bulk TS-measured band gap, consistent with the magnitude of quantum confinement predicted by the effective mass model for Q-InAs particles of this size. Different hypothetical influences on the TS data are addressed and discounted in this case, including charge hopping at the particle/particle and particle/Au interfaces, band bending in the QDs, and Coulomb blockade effect. Macroscopic I-V measurements under vacuum of Q-InAs films on Au IDA electrodes revealed the absence of any significant barrier to charge hopping at the particles' interfaces, and provided for the first time conductivity measurements for films of Q-InAs; the measured conductivity was only two orders of magnitude lower than the bulk conductivity. Other electrical studies included immobilizing Q-InAs and Q-GaAs onto metal surfaces and in conductive polymer matrices, and establishing the possibility of charge hopping between the Q-particles and the conductive matrices.; Quantum confinement effects were further explored using UV-vis absorption and photoluminescence measurements of Q-particles suspended in solution. Studies of Q-InAs suspensions revealed excitonic absorption and emission peaks blue-shifted relative to bulk absorption and photoluminescence, consistent with the presence of a molecular-like energy spectrum with a wider HOMO-LUMO separation relative to the bulk solid. The effects of material purity, the solvent used, narrowing the size distribution, and passivating the surface with capping agents on the observation of these excitonic transitions are addressed.