Study Of Quantum Structure Infrared Detector Based On Intersubband Transition

Infrared detection is used extensively for military and civilian purposes. One ofthe key technologies is infrared photodetector. The quantum well infrared detectors(QWIPs) based on intersubband transtion make use of commonly used III-V materialprocessing techniques, making fabrication of the devices easier than HgCdTe (MCT)infrared photodetectors. Also, they typically have greater radiation tolerances andquicker response than narrower band gap materials like MCT. The severaladvantages all make them to be one of the important detectors in the past30yeaes.At the same time, a new quantum structure detector which is called quantum cascadedetector (QCD) has been seriously studied for several years. QCD is also anintersubband indector which can work without bias voltage. QCD has no darkcurrent noise and thus results in a favorable noise behavior, reduced thermal load,and simpler readout circuits. Energy band engineering make the intersubbandphotodetectors to cover a detection wavelength from mid-infrared to tearhertzinfrared. The research on intersubband photodetectors will be going on in the future.In this doctoral dissertation, we mainly focus on the characteristics of intersubbandphotodetectors: QWIPs and QCDs. The details are as follows:1The structure of very long wavelength GaAs/AlGaAs QWIPs is optimized.The temperature-and bias-dependent photocurrent spectra of very long wavelengthGaAs/AlGaAs QWIPs are studied using spectroscopic measurements andcorresponding theoretical calculations. It is found that the peak response wavelengthwill shift as the bias and temperature change. Aided by band structure calculations, amodel of the double excited states is proposed and explains the experimentalobservations. In addition, the working mechanisms of the quasi-bound state confinedin the quantum well, including the processes of tunneling and thermionic emission,are also investigated in detail. It is confirmed that the first excited state, whichbelongs to the quasi-bound state, can be converted into a quasi-continuum stateinduced by bias and temperature. The bound-to-quasi-bound state transition isproved to be the best working mode in very long wavelength QWIPs.2The characteristics of a novel photovoltaic intersubband photodetector,quantum cascade detector have been studied. The design parameters, including thedoping density nsand the number of periods NQWis discussed to get a better device performance. As a conclusion, for any doping density, an ideal number of periodsmust be found. Using the In0.53Ga0.47As/In0.52Al0.48As semiconductor system, QCDdetecting at4μm is presented in mid-infrared. A responsivity of1.27mA/W and aJohnson noise limited detectivity of1.08×1011Jones are observed at77K. Also,we detailed studied the behavior of an8.9μm peak wavelength QCD based onGaAs/AlGaAs syetem and got Johnson noise limited detectivity of9.2×109Jones at77K. To obtain very long wavelength and suppresses the leakage current, aminiband-based structure is designed. The quantum design leads to15K peakresponsivity of2.34mA/W and Johnson noise limited detectivity of9×109Jones at19μm.3The design and performance of GaAs/AlGaAs terahertz QWIPs based onintersubband transition are presented. The longest detection wavelength is up to52.6μm. Large current discontinuities and instabilities have been observed within thescope of scanning voltage. It is attributed to the intersubband impact ionization. Thehigher bias caused the barrier breakdown, resulting in an electric field discontinuityat the first quantum well. With temperature increasing, the thermionic emissioncurrent becomes dominant and the current discontinuity disappears.