Effects of ion implantation on yellow luminescence in unintentional doped n-type GaN

The effects of Si, O, C and N ion implantation with different implantation doses on yellow luminescence (YL) of GaN have been investigated. The as-grown GaN samples used in the work were of unintentional doped n-type, and the photoluminescence (PL) spectra of samples had strong YL. The experimental results showed that YL of ion implanted samples exhibited marked reductions compared to samples with no implantation, while the near band edge (NBE) emissions were reduced to a lesser extent. The deep-level centers associated with YL may be produced in GaN films by O and C ion implantation, and identities of these deep-level centers were analyzed. It was also found that the dose dependence of YL was analogous with the one of the intensity ratios of YL to the near band edge (NBE) emission (I _YL /I _NBE ) for ion implanted samples. The possible reason for this comparability has been proposed.      

Effects of different ions implantation on yellow luminescence from GaN

The influence of C, N, O, Mg, Si and co-implants (Mg+Si) ions implantation with fluences in the wide range 10¹³-10¹⁷ cm⁻² on the yellow luminescence (YL) properties of wurtzite GaN has been studied by photoluminescence (PL) spectroscopy. Two types of n-type GaN samples grown by metal-organic chemical vapor deposition method (MOCVD) and labeled as No-1 and No-2 were studied. In their as-grown states, No-1 samples had strong YL, while No-2 samples had weak YL. Results of the frontside and backside PL measurements in one of the as-grown GaN epifilms are also presented. Comparing the intensity of YL between frontside and backside PL spectra, the backside PL spectrum shows the more intense YL intensity. This implies that most of the intrinsic defects giving rise to YL exist mainly near the interface between the epilayer and buffer layer. Our experimental results show that the intensity ratio of YL to near-band-edge UV emission (I_YL/I_UV) decreases gradually by increasing the C implantation fluence from 10¹³ to 10¹⁶ cm⁻² for No-1 samples after annealing at 900 °C. When the fluence is 10¹⁷ cm⁻², a distinct change of the I_YL/I_UV is observed, which is strongly increased after annealing. For No-2 samples, after annealing the I_YL/I_UV decreases gradually with increase in the C implantation fluence from 10¹³ to 10¹⁵ cm⁻². The I_YL/I_UV is gradually increased with increasing C fluence from 10¹⁶ to 10¹⁷ cm⁻² after annealing, while I_YL/I_UV for other ions-implanted GaN samples decreases monotonically with increase in the ions implantation fluences from 10¹³ to 10¹⁷ cm⁻² for both No-1 samples and No-2 samples. It is noted that for annealed C-implanted No-2 samples I_YL/I_UV is much higher than that of the as-grown one and other ion-implanted ones. In addition, I_YL/I_UV for the Mg, Si, and co-implants (Mg+Si) implanted No-2 samples with a fluence of 10¹³ cm⁻² after being annealed at 900 °C is higher than that of the as-grown one. Based on our experimental data and literature results reported previously, the origins of the YL band have been discussed.     

GaN的宽带黄光发射研究

使用非线性最优化技术，用多个高斯函数叠加最优化拟合非掺杂GaN薄膜的宽的黄色发光带. 发现宽带黄色发光带可分解为三个高斯型谱的叠加. 表明宽的黄色发光带是由三个独立辐 射跃迁发射叠加而成. 使用一种新的吸收归一化光致发光激发谱直接测量出此三个独立发射 的初始态能级，发现三个独立发射具有相同的初始态和不同的末态，并对初、末态能级的起 源作出了合理的指派. 关键词： GaN薄膜 吸收归一化光致发光激发谱 宽带黄光发射     

Structure and luminescence of a-plane GaN on r-plane sapphire substrate modified by Si implantation

We show the structural and optical properties of non-polar a-plane GaN epitaxial films modified by Si ion implantation. Upon gradually raising Si fluences from 5×10¹³ cm^-2 to 5×10¹⁵ cm^-2, the n-type dopant concentration gradually increases from 4.6×10¹⁸ cm^-2 to 4.5×10²⁰ cm^-2, while the generated vacancy density accordingly raises from 3.7×10¹³ cm^-2 to 3.8×10¹⁵ cm^-2. Moreover, despite that the implantation enhances structural disorder, the epitaxial structure of the implanted region is still well preserved which is confirmed by Rutherford backscattering channeling spectrometry measurements. The monotonical uniaxial lattice expansion along the a direction (out-of-plane direction) is observed as a function of fluences till 1×10¹⁵ cm^-2, which ceases at the overdose of 5×10¹⁵ cm^-2 due to the partial amorphization in the surface region. Upon raising irradiation dose, a yellow emission in the as-grown sample is gradually quenched, probably due to the irradiation-induced generation of non-radiative recombination centers.     

Investigation of yellow luminescence intensity of N-polar unintentionally doped GaN

This paper reports that the yellow luminescence intensity of N-polar GaN Epi-layers is much lower than that of Ga-polar ones due to the inverse polarity,and reduces drastically in the N-polar unintentionally-doped GaN after etching in KOH solution.The ratio of yellow luminescence intensity to band-edge emission intensity decreases sharply with the etching time.The full width at half maximum of x-ray diffraction of(10-12) plane falls sharply after etching,and the surface morphology characterized by scanning electron microscope shows a rough surface that changes with the etching time.The mechanism for the generation of the yellow luminescence are explained in details.     

Synthesis of GaN phase by ion implantation

GaN phase is synthesized using systemic implantation of nitrogen ions of multiple energies (290, 130 and 50 keV) into Zn-doped GaAs (1 0 0) at room temperature and subsequent annealing at 850 °C for 30 min in Ar + H₂ atmosphere. The implanted doses of nitrogen ions are 5 × 10¹⁶ and 1 × 10¹⁷ ions-cm⁻². Glancing angle X-ray diffraction studies show that hexagonal phase of GaN were formed. The photoluminescence studies show the emission from the band edge as well as from point defects.     

Origin of yellow luminescence from reduced pressure grown bulk GaN crystals

Cathodoluminescence (CL) in the scanning electron microscope has been applied to study the luminescence emission of GaN single crystals grown by LPE methods. CL spectra show the presence of near band edge and of yellow emissions. The latter has been found to be mainly related to rows of hillocks formed at the growth steps. The origin of the yellow luminescence is discussed     

Unidirectional expansion of lattice parameters in GaN induced by ion implantation

This paper reports that the 150-keV Mn ions are implanted into GaN thin film grown on Al2O3 by metal-organic chemical vapour deposition.The X-ray diffraction reciprocal spacing mapping is applied to study the lattice parameter variation upon implantation and post-annealing.After implantation,a significant expansion is observed in the perpendicular direction.The lattice strain in perpendicular direction strongly depends on ion fluence and implantation geometry and can be partially relaxed by post-annealing.While in the parallel direction,the lattice parameter approximately keeps the same as the unimplanted GaN,which is independent of ion fluence,implantation geometry and post-annealing temperature.     

HVPE外延GaN膜中黄带的光致发光激发谱研究

测量了氢化物气相外延方法生长的非特意掺杂和掺碳GaN外延膜的光致发光谱，并在光致发光谱峰位2．25eV(550nm)附近分别测量了光致发光激发谱，对两者进行了比较．从光致发光谱中发现掺碳使黄带明显增强，从光致发光激发谱中看到了掺碳引起的约3．38～2．67eV(367～465nn)范围内的特征激发带．利用CC曲线模型说明了特征激发带和黄带之间的关系，分析了黄带的可能起因．     

Amorphization and recrystallization of ion implanted Si nanocrystals probed through their luminescence properties

In this paper the amorphization of Si nanocrystals (nc) by ion beam irradiation and the subsequent recrystallization are investigated in detail. The luminescence properties of Si nanocrystals embedded within a SiO₂ matrix are used as a probe of the damaging effects generated by high-energy ion beam irradiation. Samples have been irradiated with 2 MeV Si⁺ ions at different doses, in the range between 1×10⁹ and 1×10¹⁶ cm⁻². By increasing the ion dose, the nc-related photoluminescence (PL) strongly decreases after a critical dose value. It is shown that the lifetime quenching alone cannot quantitatively explain the much stronger PL drop, but the total number of emitting centers has to diminish too. Moreover, we studied the recovery of the amorphized Si nc by performing thermal annealings. It is demonstrated that the recovery of the PL properties of completely amorphized Si nc is characterized by a single activation energy, whose value is 3.4 eV. Actually, this energy is associated to the transition between the amorphous and the crystalline phases of each Si grain. The recrystallization kinetics of Si nanostructures is demonstrated to be very different from that of a bulk system.     

Effect of the V/Ⅲ ratio during buffer layer growth on the yellow and blue luminescence in undoped GaN epilayer

Effect of the V/III ratio during buffer layer growth on the yellow and blue luminescence in undoped GaN epilayer has been studied by means of photoluminescence spectroscopy and high resolution X-ray diffraction.It is found that the densities of screw and edge threading dislocations increase with the V/III ratio of the buffer layer,and the intensities of the yellow luminescence(YL) and blue luminescence(BL) emissions also increase dramatically.However,the density ratio of the edge threading dislocation to the screw threading dislocation remains invariant,as well as the intensity ratio of YL emission to BL emission.It can be concluded from these phenomena that the edge threading dislocation and screw threading dislocation can enhance the YL and BL emissions,respectively.     

Structural modifications of AlInN/GaN thin films by neon ion implantation

To study ion beam induced modifications into MOCVD grown wurtzite AlInN layers, neon ions were implanted on the samples with four doses ranging from 10¹⁴ to 9×10¹⁵ ions/cm²$9\times {10}^{15}\text{ions}/{\text{cm}}^2$. Structural characterization was carried out by X-ray diffraction and Rutherford backscattering spectroscopy (RBS) techniques. XRD analysis revealed that GaN related peak for all samples remains at its usual Bragg position of 2θ=34.56°$2\theta =34.56\mathrm{°}$ whereas a shift in AlInN peak takes place from its position of 2θ=35.51°$2\theta =35.51\mathrm{°}$ for as-grown sample. Rutherford back scattering (RBS) analysis indicated that peak related to Ga atoms in capping layer provided evidence of partial sputtering of GaN cap layers. Moreover, Al peak position is shifted towards lower channel side and width of the signal is increased after implantation, which pointed to the inwards migration of Al atoms away from the AlInN surface. The results suggested that partial sputtering of cap layer has taken place without uncovering the underneath AlInN layer.     

MBE-grown Si: Er light-emitting structures: Effect of implantation and annealing on the luminescence properties

Features appearing in the photo-and electroluminescence spectra of light-emitting structures based on MBE-grown Si: Er layers are studied. The luminescence properties of Si layers implanted by Er and O ions were used as a reference. The temperature quenching of the photoluminescence intensity of Er-containing centers in MBE-grown and implanted layers can be approximated adequately by the same functional relationships with equal activation energies but with preexponential factors differing by more than two orders of magnitude. It is shown that the electroluminescence of Er³⁺ ions can be increased by additional coimplantation of erbium and oxygen ions into MBE-grown light-emitting diode structures and subsequent annealing. After this treatment, the Er-containing centers continue to dominate the luminescence spectrum.     

Micro-Raman and ion channeling study of crystal damage in Si induced by focused Co ion beam implantation

The lattice damage of silicon produced by ion implantation at extremely high current density of 0.8 A/cm² (2.5᎒¹⁸ cm^-2 s^-1) was investigated. In a focused ion beam system, implantation was carried out with 70 keV Co ions, fluences of 1.2᎒¹⁶ cm^-2 and 6.7᎒¹⁵ cm^-2 into Si (111) at room temperature and elevated temperatures between 355 °C and 400 °C. Radiation damage measurements were performed by Rutherford backscattering/channeling spectroscopy and micro-Raman analysis. The radiation damage was studied as a function of pixel dwell-time and implantation temperature. The critical temperature for amorphization increases with current density. Although the fluence of the focused ion implantation was constant, crystalline layers were obtained for short and amorphous layers for long pixel dwell-times. The critical dwell-time of crystalline/amorphous transition increases with implantation temperature. From the results a typical time for defect annealing of 10^-5 s at 400 °C and an activation energy of (2.5ǂ.6) eV were deduced.     

离子注入和固相外延制备Si1-x-yGexCy半导体薄膜

用等离子体增强化学气相淀积(PECVD)生长了200nm的SiGe薄膜,然后将C离子注入SiGe层,经两步热退火处理制备了Si1-x-yGexCy三元合金半导体薄膜.应用卢瑟福背散射(RBS),傅里叶变换红外光谱(FTIR)和高分辨率x射线衍射(HRXRD)研究了薄膜的结构和外延特性.发现C原子基本处于替代位置,C原子的掺入缓解了SiGe层的压应变 关键词： Si1-x-yGexCy薄膜 离子注入 固相外延     

Fabrication of contact electrodes in Si for nanoelectronic devices using ion implantation

We fabricated contact electrodes in Si for nanoelectronic device fabrication using 40 keV As ion implantation. Complete amorphization of the Si surface with contact electrodes using 400 eV Ar ion irradiation at room temperature followed by annealing at 700 °C produced Si surface with negligible SiC crystallites suitable for ultrahigh vacuum scanning tunneling microscope nanolithography. We could locate the implanted and unimplanted regions on Si and fabricate Si dangling bond wires between two contact electrodes, which is the first step for the fabrication of nanoelectronic devices in Si using UHV STM nanolithography.     

Research on the radiation hardened SOI devices with single-step Si ion implantation

Silicon-on-insulator(SOI) devices are sensitive to the total ionizing dose effect due to the existence of buried oxide.In this paper,an extra single-step Si ion implantation into buried oxide layer prior to the normal complementary metal–oxide–semiconductor transistor(CMOS) process is used to harden the SOI wafer.The top-Si quality of the hardened SOI wafer is confirmed to be good enough for device manufacturing through various characterization methods.The radiation experiments show that the total ionizing dose tolerance of the Si implanted SOI device is improved significantly.The metastable electron traps introduced by Si implantation is also investigated by electrical stress.The results show that these traps are very instable,and electrons will tunnel into or out of the metastable electron traps quickly after hot-electroninjection or hot-hole-injection.