同電子性銦摻雜對P型氮化鎵薄膜之光特性研究

Abstract

在本論文中，我們利用XRC、冷激光光譜(Photoluminescence, PL)、冷激光激發光譜(Photoluminescence excitation, PLE)、拉曼光譜(Raman)等方法，研究鎂、銦共同摻雜之氮化鎵薄膜的光學特性。未經熱退火的鎂、銦摻雜之氮化鎵薄膜，其冷激光光譜出現兩個發光頻譜，分別在2.88eV與3.18eV，其伴隨的振盪頻譜是由干涉效應產生。當樣品只摻雜鎂(CP2Mg=250sccm)，其冷激光光譜由2.88eV主導；當樣品共同摻雜鎂(CP2Mg=250sccm)與銦(TMIn=100sccm)時，3.18eV漸增強；當銦的流率為250sccm(TMIn=250sccm)時，3.18eV最強。由變化激發強度的PL光譜得知，2.88eV的躍遷機制屬於施子–受子對的躍遷(DAP)；3.18eV則是電導帶到受子的躍遷(eA)，此兩個躍遷皆牽涉與Mg相關的受子能階，一為深層Mg的復合物(deep Mg complex, dMg)；另一為一般較淺層Mg的受子(common Mg acceptors, Mg0)。藉熱退火(TA)在750oC，60分鐘的活化處理，由二次離子質譜儀(SIMS)的量測知，鎂的濃度分佈在2.69 ~ 3.49x1019cm-3 之間。且由SIMS與霍爾(Hall)的量測得知，摻雜鎂(CP2Mg=250sccm)與銦(TMIn=250sccm) 的樣品，其電洞活化率最高；此樣品的拉曼光譜與XRC之半高寬最窄，PL光譜也如同拉曼光譜與XRC都有相同趨勢，在此銦的流率呈現較特殊的行為。為了進一步瞭解亞穩態(metastable)的行為，我們針對此樣品作另外的分析，監測冷激光光強度在低溫時隨時間的變化情形。不同波長的強度皆隨著時間慢慢衰減，依其衰減時間常數的不同，可分為兩個部份：第一部份為380nm ~ 400nm，其時間常數約為1000秒；第二部份為410nm ~ 460nm，其時間常數約為100秒。只摻雜鎂(CP2Mg=250sccm)的樣品，衰減時間常數也可分為兩個部份：380nm ~ 400nm，其時間常數約為30秒；410nm ~ 460nm，其時間常數約為100秒。這顯示共同摻雜In、Mg之GaN的鎂相關淺層受子能階(Mg0)上的能態密度多於只摻雜Mg之GaN。同時，我們也量測共同摻雜In、 Mg之GaN，其中400nm在不同溫度冷激光光強度隨時間的變化，再由阿瑞尼士圖推算出介於鎂相關的淺層受子能階(Mg0)與深層受子能階(dMg)間的活化能約為103meV，此值大於未摻雜In樣品的69meV，這表示摻入In後增加了一些位能障。

The optical properties and metastable behavior of Mg-In codoped GaN thin films (grown on sapphire) were characterized by photoluminescence (PL), photoluminescence excitation (PLE), Raman spectra and X-ray diffraction. The PL spectra of as-grown Mg-In codoped GaN show two emission peaks around 2.88eV and 3.18eV with oscillations due to the microcavity interference effect. For the sample doped with Mg only (CP2Mg=250sccm), the 2.88eV band dominates the PL spectrum. For the sample codoped with Mg and In (CP2Mg:250sccm+TMIn:100sccm), the PL spectrum begins to show the 3.18eV band. When the TMIn flow rate increases to 250 sccm, the 3.18eV band becomes the most intense. We also measured the excitation power dependence of PL spectra, in which the 2.88eV band can be attribuited to the Donor-Acceptor-Pair recombination (DAP) and the 3.18eV band is attribuited to the free to bound recombination (eA). These two transitions involve Mg-related acceptors, one is the deep Mg complex (dMg); the other is the common Mg acceptors (Mg0). The sample activation was treated by thermal annealing (TA) at 750 oC for 60 min. The Mg concentrations were determined to be from 2.69x1019cm-3 to 3.49x1019cm-3 by secondary ion mass spectrometry (SIMS) measurements. From the SIMS and the Hall measurements, the sample codoped with Mg and In (CP2Mg:250sccm+TMIn:250sccm) also exhibits the best activation efficiency. Furthermore, the FWHMs of the Raman spectra and XRC are the narrowest. The PL spectra show the similar trend as the Raman and XRC spectra. Besides, the special metastable behavior was observed in this sample. In order to understand the temporal behavior of two Mg-related emission bands, we carried out the measurements of PL intensity evolution. There are two categories by analyzing the distribution of decay time constants: one is for emissions from 380 nm to 400 nm having time constant on the order of ~ 1000 seconds; the other is for emissions from 410 nm to 460 nm with time constant on the order of ~ 100 seconds. For the sample doped with Mg only (CP2Mg=250sccm), the time constant for emissions from 380 nm to 400 nm is on the order of ~ 30 seconds; and that for emissions from 410 nm to 460 nm is on the order of ~ 100 seconds. Our results indicate that the density of state responsible for the 3.18eV emission band (Mg0) in GaN:(Mg+In) is more than that in GaN:Mg. In addition, we have also measured the PL intensity of GaN:(Mg+In) at 400 nm as a function of temperature and obtained an optical potential barrier between the common Mg acceptors (Mg0) and Mg related deep levels (dMg) to be about 103meV from the Arrehenius plot. It is greater than 69meV for GaN:Mg, and indicates that In could introduce larger potential barrier in GaN:Mg sample.