Control of the morphology of InGaN/GaN quantum wells grown by metalorganic chemical vapor deposition (original) (raw)
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Journal of Crystal Growth, 1998
InGaN/GaN single and multi quantum wells have been grown by metal-organic chemical vapor deposition, varying the growth rate of well and barrier layers as well as the Si-doping of the GaN barriers. Separately, the effect of these growth parameters on the surface morphology of thin GaN and InGaN layers grown under the same conditions had been studied. The surface morphology of the layers strongly influenced the structural properties of the multi quantum wells. The optical properties seemed to be less affected by the observed layer thickness fluctuations in the 200-500 nm range rather than by variations in the indium composition on a shorter length scale.
Thin Solid Films, 2006
InGaN/GaN multiple quantum well light emitting diode structures have been grown on sapphire substrates by metalorganic chemical vapor deposition. They are investigated, in this study, by high-resolution X-ray diffraction, high-resolution transmission electron microscopy, photoluminescence, and photoluminescence excitation. HR-XRD showed multiple satellite peaks up to 10th order due to the quantum well superlattice confinement effects. These indicate the high quality of layer interface structures of this sample. Excitation power-dependent photoluminescence shows that both piezoelectric field-induced quantum-confined Stark effect and band filling effect influence the luminescent properties of this sample. Temperature-dependent photoluminescence of this sample has also been studied. The peak position of the PL exhibits a monotonic red-shift and the full width at half maximum of the PL band shows a W-shaped temperature-dependent behavior with increasing temperature. From the photoluminescence excitation results, a large energy difference, so-called Stokes shift, between the band-edge absorption and emission was observed.
Microstructural characterization of InGaN/GaN multiple quantum wells with high indium composition
Journal of Crystal Growth, 2001
The microstructural study of InGaN/GaN multiple quantum well (MQW) structures with high In (indium) composition (>30%) has been performed using transmission electron microscopy (TEM). The increased strain in InGaN/GaN MQWs by high In composition is relaxed by the formation of several defects such as dislocations, stacking faults, V-defects, and tetragonal shape defects. High-resolution TEM (HRTEM) measurement shows a new formation mechanism of V-defects, which is related to the stacking mismatch boundary induced by stacking faults. These Vdefects result in different growth rates of the GaN barriers according to the degree of the bending of InGaN well layers, which changes the period thickness of the superlattice. In addition, evidence of In clustering is directly observed both by using an In ratio map of the MQWs and from In composition measurements along an InGaN well using energy filtered TEM (EFTEM). r
Journal of Crystal Growth, 2011
InGaN/GaN quantum wells (QWs) with symmetrical ultra thin (about 0.5nm) low temperature GaN (LT-GaN) layers bounding each InGaN layer were grown by metal-organic vapor phase epitaxy (MOVPE). From the high resolution X-ray diffraction (HR-XRD) measurement, it showed improved well-barrier interface abruptness compared to the reference MQWs without the LT-GaN layers. In addition, the V-defect density and surface roughness were reduced, especially with the depth of V-defect as low as 0.7nm. Based on the temperature dependence photoluminescence (TDPL) experiments, the internal quantum efficiency (IQE) was increased from 21.2% to 30.1% by inserting the LT-GaN layers. The carrier lifetime obtained from room temperature time resolved photoluminescence (TRPL) measurement was 7.95ns, which was longer than 5.34ns for reference MQWs. These results indicated that these additional symmetrical thin LT-GaN layers enhanced the mobility of indium and gallium atoms as well as suppressed the indium desorption for growth high quality InGaN layers and in turn improved its structural and luminescence properties.
Secrets of GaN substrates properties for high luminousity of InGaN quantum wells
Violet and blue Laser diodes, as well as highly efficient high-power Light Emitting Diodes (including any UV emitters) can be constructed using low-dislocation-density freestanding GaN substrates, either produced as thick HVPE layers on foreign substrates, or using direct methods of crystallization as ammonothermal one or high pressure growth from the nitrogen solution in gallium. This paper shows some of the most most important issues concerning application of such substrates. The first issue is the choice of the substrate thickness influencing the accommodation of strain, cracking and bowing of the samples. In this point, a new way of prestressing the substrate by lateral patterning will be presented. The second issue is the surface preparation either by mechanical polishing and reactive ion etching, or mechano-chemical polishing, in particular, a distribution of defects revealed by chemical etching will be discussed. Finally, the problem of substrate misorientation influencing the further morphology and indium incorporation into InGaN quantum wells will be shown. For higher misorientation of the substrates, the incorporation of indium decreases , but at the same time, the fluctuations of indium increase giving blue-shifted, weaker and broader photoluminescence peaks.
Secrets of GaN substrates properties for high luminousity of InGaN quantum wells
Light-Emitting Diodes: Research, Manufacturing, and Applications XII, 2008
Violet and blue Laser diodes, as well as highly efficient high-power Light Emitting Diodes (including any UV emitters) can be constructed using low-dislocation-density freestanding GaN substrates, either produced as thick HVPE layers on foreign substrates, or using direct methods of crystallization as ammonothermal one or high pressure growth from the nitrogen solution in gallium. This paper shows some of the most most important issues concerning application of such substrates. The first issue is the choice of the substrate thickness influencing the accommodation of strain, cracking and bowing of the samples. In this point, a new way of prestressing the substrate by lateral patterning will be presented. The second issue is the surface preparation either by mechanical polishing and reactive ion etching, or mechano-chemical polishing, in particular, a distribution of defects revealed by chemical etching will be discussed. Finally, the problem of substrate misorientation influencing the further morphology and indium incorporation into InGaN quantum wells will be shown. For higher misorientation of the substrates, the incorporation of indium decreases , but at the same time, the fluctuations of indium increase giving blue-shifted, weaker and broader photoluminescence peaks.
Structural and optical properties of InGaN/GaN layers close to the critical layer thickness
Applied Physics Letters, 2002
Structural and optical properties of InGaN / GaN multiple quantum wells ͑MQWs͒ grown on nano-air-bridged GaN template by metal organic chemical vapor deposition were investigated. The InGaN / GaN MQWs on nano-air-bridged GaN demonstrate much better surface morphology, revealing low defect density ϳ4 ϫ 10 8 cm −2 with step flow features measured by atomic force microscopy. The photoluminescence measurement shows one magnitude higher in intensity from less defective InGaN MQWs compared to that of the control InGaN MQWs. The improvement in photoluminescence of the InGaN MQWs is benefited from the reduction of threading dislocation density in the InGaN / GaN active layers and GaN template, revealed from cross-sectional transmission electron microscopy. High resolution x-ray diffraction analysis results show higher indium mole fraction in the MQWs when grown on nano-air-bridged GaN template, due to the strain relaxation in the nano-air-bridged GaN template. This higher indium incorporation is consistent with the redshift of the photoluminescence peak.
High resolution transmission electron microscopy has been employed to investigate the impact of the GaN barrier growth technique on the composition profile of InGaN quantum wells (QWs). We show that the profiles deviate from their nominal configuration due to the presence of an indium tail at the upper interface of the QW. This indium tail, thought to be associated with a segregation effect from the indium surfactant layer, has been shown to strongly depend on the growth method. The effect of this tail has been investigated using a self-consistent Schrödinger–Poisson simulation. For the simulated conditions, a graded upper interface has been found to result in a decreased electron-hole wavefunction overlap of up to 31% compared to a QW with a rectangular profile, possibly leading to a decrease in radiative-recombination rate. Therefore, in order to maximize the efficiency of a QW structure, it is important to grow the active region using a growth method which leads to QW interfaces which are as abrupt as possible. The results of this experiment find applications in every study where the emission properties of a device are correlated to a particular active region design.
Journal of Electronic Materials, 2007
In this report, the influence of magnesium doping on the characteristics of InGaN/GaN multiple quantum wells (MQWs) was investigated by means of atomic force microscopy (AFM), photoluminescence (PL), and X-ray diffraction (XRD). Five-period InGaN/GaN MQWs with different magnesium doping levels were grown by metalorganic chemical vapor deposition. The AFM measurements indicated that magnesium doping led to a smoother surface morphology. The V-defect density was observed to decrease with increasing magnesium doping concentration from 109cm−2(nodoping)to10 9 cm-2 (no doping) to 109cm−2(nodoping)to10 6 cm-2 (Cp 2 Mg: 0.04 sccm) and further to 0 (Cp 2 Mg: 0.2 sccm). The PL measurements showed that magnesium doping resulted in stronger emission, which can be attributed to the screening of the polarization-induced band bending. XRD revealed that magnesium doping had no measurable effect on the indium composition and growth rate of the MQWs. These results suggest that magnesium doping in MQWs might improve the optical properties of GaN photonic devices.