MgZnO异质结紫外光电探测器件的制备与内增益特性研究
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摘要
MgZnO薄膜具有带隙可调范围宽（3.3eV至7.8eV可调），外延生长温度低，抗辐射能力强及其它优良的紫外光电性能，近年来成为了紫外探测领域的研究热点之一。然而，目前高Mg组分MgZnO基紫外光电探测器面临着量子效率较低及缺少可控内增益过程的发展难题。本论文针对这一难题，在分析其物理原因基础之上，开展了高Mg组分立方MgZnO薄膜n型掺杂、Si(111)衬底单一立方相MgZnO薄膜外延生长、梯度带隙立方MgZnO/p-Si异质结紫外光电探测器件制备等工作，并对材料特点及器件性能进行了研究，主要研究工作如下：
一、针对带隙处于日盲区的立方MgZnO薄膜电阻率过高而使得光生载流子在弱的内建电场强度下不易分离的难题，提出带隙展宽施主型缺陷能级深化，使得材料载流子浓度过低的推断，选用Ga作为n型掺杂源，成功获得电阻率相对较低的立方MgZnO薄膜。在此基础上制备了肖特基MSM型MgZnO日盲紫外探测器，并对器件的性能进行了测试和分析；
二、利用低压金属有机气相沉积(LP-MOCVD)，开展了Si(111)衬底外延生长单一立方相MgZnO薄膜的工作。MgZnO合金能带调节中导带及价带移动幅度差较大，可使得梯度带隙MgZnO中电子受到附加准电场，更易碰撞离化，结合这一物理思想，制备了光伏型单层梯度带隙n-MgZnO/p-Si异质结日盲紫外探测器，对器件光生载流子倍增的过程进行了研究；
三、利用等离子体辅助的分子束外延(RFPAMBE)设备，通过周期性改变Zn源束流，获得了界面陡峭的多层梯度带隙MgZnO/p-Si异质结日盲紫外探测器，器件具有较好的日盲波段敏感性，响应峰值在250nm附近，响应度随偏压的增加呈现出由于载流子倍增而造成的非线性增长特点。
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.
一、针对带隙处于日盲区的立方MgZnO薄膜电阻率过高而使得光生载流子在弱的内建电场强度下不易分离的难题，提出带隙展宽施主型缺陷能级深化，使得材料载流子浓度过低的推断，选用Ga作为n型掺杂源，成功获得电阻率相对较低的立方MgZnO薄膜。在此基础上制备了肖特基MSM型MgZnO日盲紫外探测器，并对器件的性能进行了测试和分析；
二、利用低压金属有机气相沉积(LP-MOCVD)，开展了Si(111)衬底外延生长单一立方相MgZnO薄膜的工作。MgZnO合金能带调节中导带及价带移动幅度差较大，可使得梯度带隙MgZnO中电子受到附加准电场，更易碰撞离化，结合这一物理思想，制备了光伏型单层梯度带隙n-MgZnO/p-Si异质结日盲紫外探测器，对器件光生载流子倍增的过程进行了研究；
三、利用等离子体辅助的分子束外延(RFPAMBE)设备，通过周期性改变Zn源束流，获得了界面陡峭的多层梯度带隙MgZnO/p-Si异质结日盲紫外探测器，器件具有较好的日盲波段敏感性，响应峰值在250nm附近，响应度随偏压的增加呈现出由于载流子倍增而造成的非线性增长特点。
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.
引文
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