The Fabrication And Internal Gain Properties Of MgZnO-Based Heterostructures Ultraviolet Detectors

As a member of group II-VI wide-band-gap semiconductors, MgxZn1-xO alloysare generating considerable interest as they can provide, in principle, an accessibleband-gap range from around3.37eV (ZnO) to7.8eV (MgO). This makes thempromising candidates for deep ultraviolet (DUV) optoelectronic devices. In the pastdecade, a large number of experiments have been conducted, focusing on solar-blindphotodetection using MgZnO films, because of various important applications inmissile tracking, flame detection, ozone layer monitoring, and so on. To date,however, most of the solar-blind photodetectors based on MgZnO havelow-performance, especially in responsivity, which is one of the important figures ofmerit for DUV detectors to be commercially applied. Consequently, a controllableand high gain mechanism is required. This work foucs on the aforementionedproblem, the main results were obtained as follows:1. The gallium (Ga) doped cubic MgZnO films, which have been grown bymetal organic chemical vapor deposition, have been obtained. It wasdemonstrated that Ga doping improves the n-type conduction of the cubicMgZnO films. A two-orders of magnitude enhancement in lateral n-typeconduction have been achieved for the cubic MgZnO films. The responsivity of the cubic MgZnO-based photodetector has been also enhanced. Depletionregion electric field intensity enhanced model was adopted to explain theimprovement of quantum efficiency in Ga doped MgZnO-based detectors.2. For MgxZn1-xO alloys, due to the wide tunable bandgap and a larger ratio ofconduction-band offset to valence-band offset (ΔEC/ΔEV), it is very suitablefor photon detection by using graded-band-gap technique. Via constructingheterojunctions based on p-Si/i-MgO/Graded-Band-Gap-Cubic-MgZnO, asolar-blind photodetector with enhanced and tunable gain have beendemonstrated. The photodetector showed high performance, namely, highresponsivity (1160mA/W), quantum efficiency (600%), high sensitivity andselectivity towards the solar-blind spectrum, and fast response times (~15μs).3. A solar blind photodetector based on multilayers graded band gapcubic-MgZnO/i-MgO/p-Si has been demonstrated. The device exhibits ahigh responsivity wich is attributed to the photo-generated carriers impactionization. This device structure will be more valuable in the field oflow-noise solar-blind detection for its significant band alignment differentbetween the conduction band and valence band.