Liang Junwu

Growth of AlGaN Epitaxial Film with High Al Content by Metalorganic Chemical Vapour Deposition

A high-Al-content AlGaN epilayer is grown on a low-temperature-deposited AlN buffer on (0001) sapphire by low pressure metalorganic chemical vapour deposition. The dependence of surface roughness, tilted mosaicity, and twisted mosaicity on the conditions of the AlGaN epilayer deposition is evaluated. An AlGaN epilayer with favourable surface morphology and crystal quality is deposited on a 20 nm low-temperature-deposited AlN buffer at a low V/III flow ratio of 783 and at a low reactor pressure of 100 Torr, and the adduct reaction between trimethylaluminium and NH3 is considered.

A surface kinetics model for the growth of Si1-xGex by UHV/CVD using SiH4/GeH4

The surface reaction mechanism of Si1-xGex/Si growth using SiH4 and GeH4 in UHV/CVD system was studied. The saturated adsorption and desorption of SiH4 from Si(1 0 0) surface was investigated with the help of TPD and RHEED, and it was found that all the 4 hydrogen atoms of one SiH4 molecule were adsorbed to the Si surface, which meant that the dissociated adsorption ratio was proportional to 4 power of surface vacancies. The analysis of the reaction of GeH4 was also done. A new surface reaction kinetic model on Si1-xGex/Si epitaxial growth under UHV conditions by SiH4/GeH4 was proposed based on these studies. The predictions of the model were verified by the experimental results

Measurement of trace phosphorus in dichlorosilane by high-temperature hydrogen reduction gas chromatography

Abstract Dichlorosilane, a gas at normal temperature with a boiling point of 8.3°C, is very difficult to sample and detect using conventional methods. We reduced phosphorus in dichlorosilane to PH3 by hydrogen at high temperature, then PH3 was separated from chlorosilanes by NaOH solution and from other hydrides by chromatographic absorption. Thus the problem of interference of chlorosilanes and other hydrides was overcome and PH3 was measured by a double flame photometric detector at 526 nm. This method was sensitive, reliable and convenient and the sensitivity reached as low as 0.04 μg/l.

Continuous-Wave Operation of GaN Based Multi-Quantum-Well Laser Diode at Room Temperature

Room-temperature operation of cw GaN based multi-quantum-well laser diodes (LDs) is demonstrated. The LD structure is grown on a sapphire (0001) substrate by metalorganic chemical vapour deposition. A 2.5 mu m x 800 mu m ridge waveguide structure is fabricated. The electrical and optical characteristics of the laser diode under direct current injection at room temperature are investigated. The threshold current and voltage of the LD under cw operation are 110mA and 10.5V, respectively. Thermal induced series resistance decrease and emission wavelength red-shift are observed as the injection current is increased. The full width at half maximum for the parallel and perpendicular far field pattern (FFP) are 12 degrees and 32 degrees, respectively.

Crystallographic tilt in GaN layers grown by epitaxial lateral overgrowth

The crystallographic tilt in GaN layers grown by epitaxial lateral overgrowth (ELO) on sapphire (0001) substrates was investigated by using double crystal X-ray diffraction (DC-XRD). It was found that ELO GaN stripes bent towards the SiNx mask in the direction perpendicular to seeding lines. Each side of GaN (0002) peak in DC-XRD rocking curves was a broad peak related with the crystallographic tilt. This broad peak split into two peaks (denoted as A and B), and peak B disappeared gradually when the mask began to be removed by selective etching. Only narrow peak A remained when the SiNx mask was removed completely. A model based on these results has been developed to show that there are two factors responsible for the crystallographic tilt: One is the non-uniformity elastic deformation caused by the interphase force between the ELO GaN layer and the SiNx mask. The other is the plastic deformation, which is attributed to the change of the threading dislocations (TDs)—from vertical in the window regions to the lateral in the regions over the mask.

Growth of GaAs on Si by Using a Thin Si Film as Buffer Layer

We report a novel technique for growing high-quality GaAs on Si substrate. The process involves deposition of a thin amorphous Si film prior to the conventional two-step growth. The GaAs layers grown on Si by this technique using metalorganic chemical vapor deposition exhibit a better surface morphology and higher crystallinity as compared to the samples grown by conventional two-step method. The full width at half maximum (FWHM) of the x-ray (004) rocking curve for 2.2 μm thick GaAs/Si epilayer grown by using this new method is 160 arcsec. The FWHM of the photoluminescence spectrum main peak for this sample is 2.1 meV. These are among the best results reported so far. In addition, the mechanism of this new growth method was studied using high-resolution transmission electron microscopy.

The dependence of GexSi1-x epitaxial growth on GeH4 flow using chemical vapour deposition

GexSi1-x epilayers were grown at 700–900°C by atmospheric pressure chemical vapour deposition. GexSi1-x, Si and Ge growth rates as functions of GeH4 flow are considered separately to investigate how the growth of the epilayers is enhanced. Arrhenius plots of Si and Ge incorporation in the GexSi1-x growth show the activation energies associated with the growth rates are about 1.2 eV for silicon and 0.4 eV for germanium, indicating that Si growth is limited by surface kinetics and Ge growth is limited by mass transport. A model based on this idea is proposed and used to simulate the growth of GexSi1-x. The calculation and experiment are in good agreement. Growth rate and film composition increase monotonically with growth pressure; both observations are explained by the model.

Epitaxial growth of high purity GaAs in an argon atmosphere

Abstract The epitaxial growth of high purity GaAs has been carried out successfully with a leak-free and corrosion resistant AsCl 3 -Ga-Ar system. A background free carrier concentration of 7.35 × 10 12 cm -3 , a mobility of 2.05 × 10 5 cm 2 /V · s at 77 K, a peak mobility of 3.78 × 10 5 cm 2 /V · s at 35 K and a thickness of 18.0 μm were achieved by careful control of growth conditions. The effects of deposition temperature on the growth rate and mobility at 77 K were investigated in H 2 , N 2 and Ar systems respectively. It was found that the Ar system has an advantage over the N 2 system in growing high purity GaAs, especially in growing thinner epilayers. The residual impurities in high purity epilayers were investigated by IMMA and photoluminescence measurements. By these analyses one can see that the Si contamination is suppressed in the Ar system as effectively as in the N 2 system, and the dominat residual acceptor impurity of the high purity epilayer grown in the Ar system is carbon.