H.B. Yu

Determination of twist angle of in-plane mosaic spread of GaN films by high-resolution X-ray diffraction

X-ray diffraction (XRD) measurements of Phi scan in different chi angle in skew geometry for GaN films have shown that the peak widths of Phi scan decrease with the increment of angle chi. The FWHM of omega scan also increases with the inclination angle and reaches to be equal until the reflection plane is perpendicular to the surface of the sample. Based on these measured results, we developed a method to determine directly the twist angle of un-doped and Si-doped GaN films grown on c-sapphire substrates by MOCVD

Dependence of leakage current on dislocations in GaN-based light-emitting diodes

The reverse bias current-voltage (I–V) characteristics of GaN-based light-emitting diodes (LEDs) were investigated. The leakage current exhibits exponential dependence on the bias voltage with different exponents for various voltage ranges. The leakage current is closely related to the density of dislocations. The number of dislocations in GaN was determined by atomic force microscopy combined with hot H3PO4 etching. Dislocations with a screw component in the GaN films were found to have a strong influence on the reverse leakage current of LEDs. The dislocation electrical activity in GaN grown on c-plane sapphire is different from that in GaN grown on a-plane sapphire.

Influence of the deposition time of barrier layers on optical and structural properties of high-efficiency green-light-emitting InGaN∕GaN multiple quantum wells

We reported the effect of the deposition time of barrier layers on optical and structural properties of high-efficiency green-light-emitting InGaN∕GaN multiple quantum wells (MQWs) by photoluminescence (PL) and high-resolution x-ray diffraction techniques. The MQW samples on (0001)-plane sapphire substrates were prepared with a ramping method by metalorganic chemical deposition. It was found that the structural or interface quality of the MQW system improved as the deposition time of barrier layers increased from 10 to 14min, but lattice relaxation was still observed. The relaxation degree decreases from 33% to 6% as the deposition time increases. Temperature-dependent PL measurements from 12 to 300K indicated that the integrated PL intensities start to decay rapidly as temperature rises above 50K for the sample with the shorter deposition time, and above 100K for the sample with the longer deposition time. The luminescence thermal quenching of the two samples suggests the two nonradiative recombination c...

Effects of TMIn flow rate of barrier layer on the optical and structural properties of InxGa1-xN/InyGa1-yN multiple quantum wells

We reported the effect of trimethylindium (TMIn) flow rate in the barrier layer on the structural and optical properties of InxGa1-xN/InyGa1-yN multiple quantum wells (MQWs) grown on (0001)-oriented sapphire substrates by low-pressure metalorganic chemical deposition (LP-MOCVD). It was found that the change of TMIn flow rate dramatically influences the interface quality and optical properties. Temperature-dependent photoluminescence (PL) and high-resolution X-ray diffraction (HRXRD) measurements provide proof evidence that the increment of TMIn flow rate deteriorates the interfacial abruptness, decreases the emission wavelength (blue shift) and the efficiency of nonradiative recombination process

Effects of ammonia flow at growth temperature ramping process on optical properties of InGaN/GaN multiple quantum wells

Different ammonia flow rates were used during temperature ramping up to 1050°C after InGaN/GaN multiple quantum wells (MQWs) were grown at 820°C. Temperature-dependent photoluminescence (PL) as well as time-resolved PL (TRPL) spectra were measured and higher optical efficiency was obtained when higher ammonia flow rates were used. The effects of ammonia flow on the optical properties of InGaN/GaN multiple quantum wells were attributed to different indium content redistribution. At lower ammonia flow, In-rich regions became more uniform while the number of the In-rich regions decreased as a result of the disappearance of some In-rich regions with less In-rich regions. We ascribed enhancement of desorption of indium atoms to the lower ammonia flow.

Quantitative study of carbon doping of GaAs grown by metalorganic vapor-phase epitaxy

Abstract Based on the analysis of experimental data from the atmospheric-pressure-metalorganic vapor-phase epitaxy (AP-MOVPE) of carbon-doped GaAs, using trimethylgallium (TMGa) and arsine (AsH 3 ) as growth precursors and carbon tetrachloride (CCl 4 ) as dopant precursor, the quantitative relation between control parameters, namely growth temperature and flow rates of CCl 4 and AsH 3 , and hole concentration has been investigated and established, which is p =5×10 8 F CCl 4 F −1.5 AsH 3 exp(2×10 5 / RT g ), with the flow rate of TMGa kept constant at 0.78 SCCM. Since this deduction was fully based on the experimental data obtained, the result can well demonstrate the existing doping characteristics, and also agree with the scattered individual expressions previously reported. Finally, an improved CCl 4 -doping mechanism for the MOVPE growth of GaAs has been presented.

Characterization of carbon-doped GaAs grown by metalorganic vapor-phase epitaxy

Abstract For carbon-doped p-GaAs layers grown by metalorganic vapor-phase epitaxy (MOVPE), the two parameters, k and α, respectively, used for indicating strain state and activity ratio of the C-doped epilayers, are important for demonstrating the quality of GaAsxa0:xa0C layers. By comparing the data from Hall effect and double-crystal X-ray diffraction (DCXRD) measurements made on as-grown and annealed GaAsxa0:xa0C layers grown by atmospheric pressure MOVPE (AP-MOVPE) using trimethylgallium (TMGa), arsine (AsH3) and carbon tetrachloride (CCl4), the lattice mismatch and resultant strain state, and hydrogen passivation of GaAsxa0:xa0C layers on GaAs substrates were investigated as well as their changes after annealing. Furthermore, a relation was established between the lattice mismatch (Δa⊥/aGaAs) and hole concentration p (cm−3), Δa⊥/aGaAs=−8×10−24kp/α. With this equation the relation between k and α can be determined from the relation between the measured (Δa⊥/aGaAs) and p. If one of the two parameters, k and α, is known, the other could be just then determined. This method for determining the values of both k and α, not involving the traditional use of the secondary ion mass spectrometry (SIMS), is not only relatively simple and cheap, but also in fairly good agreement with the experimental results.