Prototype Fabrication Research of Ultra-sensitive Optical Sensor Using Charging Effect of Quantum Dots

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We have investigated the electronic states of self-assembled InAs dots through electron tunneling spectroscopy and conductance spectroscopy. Both types of measurements were performed based on the built-in device structures which were specially designed together with the self-assembled quantum dots. Both methods plays crutial role to investigate electronic states in the self assembled InAs dots because electron states can be directly monitored unlike commonly performed optical methods such as the photoluminescence measurements. Major results are listed as follows. (I) In order to clarify the effects of dot size variations on the performance of high resolution sensors based on charging effects, we have verified electronic states (1s-like, 1p-like, 1d-like, 2s-like states) and their magnetic fields dependence and that the variations were well resolved by the present electron tunneling method. The average wave function extent in the dots were estimated by the observation of diamagnetic shi … More fts and the results were well accounted for by the estimation based on the dot size estimated by the AFM measurements. The tunneling spectroscopy results were found to be consistent with the far-infrared absorption experiment which were performed by Professor Hirakawa who is one of the member investigators of the present projects. (ii) In order to overcome the size variation effects of the quantum dots, we have proposed and investigated the new device structure which contains several thousands of dots in one device and measures averaged "single dot" states through channel conductance. In addition to the the feature of aviding the dot size variation, the present device structure has also an advantage of increasing the small scattering cross-sections which is the major weakness of the ultra-sensitive optical sensors using charging effects. The present device was verified to be sensitive enough to monitor the electron charging states of an average "single dot". This was the first demonstration to observe shell structures by the built-in conductance methods using heterojunction transistor structures. Less