LT-AlN Interlayers Research Articles

MOVPE growth conditions optimization for AlGaN/GaN/Si heterostructures with SiN and LT-AlN interlayers designed for HEMT applications

In this work we present the influence of in situ deposited non-continous SiN layer and the chemical precursors III/V mole ratio change during GaN buffer growth for AlGaN/GaN/Si(111) heterostructures with low temperature AlN interlayer on their crystalline quality and electrical mobility of two dimensional electron gas (2DEG). We show, that application of SiN layer resulted in a decrease of (0002) full width at half maximum of diffraction peak below 400 arcsec and build-in stress in 2 µm thick heterostructures below 200 MPa without any relaxation visible on the surface. In optimized AlGaN/GaN heterostructures, by altering V/III mole ratio during growth of GaN subbuffer, the maximum 2DEG mobility of 2057 cm2 V−1 s−1, measured by impedance spectroscopy method, was obtained.

Optimization of AlGaN/GaN/Si(111) buffer growth conditions for nitride based HEMTs on silicon substrates

In this work we present results regarding growth of AlGaN/GaN/Si(111) HEMTs for integration of high frequency microelectronics with a silicon platform. GaN buffers with thicknesses above 1μm were grown using one or two low temperature LT-AlN interlayers. The impact of the number of LT-AlN interlayers as well as the influence of the V/III ratio during growth of the GaN buffer, on the surface morphology and electrical parameters of AlGaN/AlN/GaN/Si(111) heterostructures were studied.Obtained results show that application of low temperature AlN interlayers during growth of GaN on Si(111) is a valuable method of stress reduction in the deposited GaN layer and thus extends its critical thickness. However, deposition of a LT-AlN layer leads to a surface roughness and a decrease of GaN buffer resistivity. Growth of the GaN buffer with high V/III ratio enhances the buffer resistivity, 2DEG mobility and sheet carrier concentration. Optimized AlGaN/AlN/GaN/Si(111) heterostructure has similar mobility and sheet carrier concentration as a reference AlGaN/AlN/GaN heterostructure grown on sapphire.

Morphology and microstructure evolution of AlxGa1−xN epilayers grown on GaN/sapphire templates with AlN interlayers observed by transmission electron microscopy

Morphology and microstructure evolution of Al0.3Ga0.7N epilayers grown on GaN/sapphire templates with low-temperature (LT) AlN interlayers (IL) by means of metal organic chemical vapor deposition have been investigated by transmission electron microscopy and atomic force microscopy. It is found that the IL improves the surface morphology and suppresses edge-type threading dislocations (TDs). When the IL thickness is 20nm, there is the lowest density of the edge-type TD with 8.7×108cm−2. However, the edge-type TD density increases somewhat as IL thickness increases to 40nm. It is believed that two mechanisms determine the microstructure evolution of the AlxGa1−xN epilayers. One is the TD suppression effect of LT-AlN ILs that ILs can provide an interface for edge-type TD termination. Another is the TD introduction effect of ILs that new edge-type TDs are produced. Due to the lattice mismatch between AlN, GaN, and AlxGa1−xN, the strain in AlxGa1−xN epilayers is modified by inserting the AlN IL, and thus changes the formation of the edge-type TDs.

Metalorganic chemical vapor phase epitaxy of gallium‐nitride on silicon

GaN growth on Si is very attractive for low-cost optoelectronics and high-frequency, high-power electronics. It also opens a route towards an integration with Si electronics. Early attempts to grow GaN on Si suffered from large lattice and thermal mismatch and the strong chemical reactivity of Ga and Si at elevated temperatures. The latter problem can be easily solved using gallium-free seed layers as nitrided AlAs and AlN. The key problem for device structure growth on Si is the thermal mismatch leading to cracks for layer thicknesses above 1 μm. Meanwhile, several concepts for strain engineering exist as patterning, Al(Ga)N/GaN superlattices, and low-temperature (LT) AlN interlayers which enable the growth of device- relevant GaN thicknesses. The high dislocation density in the heteropitaxial films can be reduced by several methods which are based on lateral epitaxial overgrowth using ex-situ masking or patterning and by in-situ methods as masking with monolayer thick SiN. With the latter method in combination with strain engineering by LT-AlN interlayers dislocation densities around 109 cm−2 can be achieved for 2.5 μm thick device structures.

Comparison of various buffer schemes to grow GaN on large-area Si(111) substrates using metal-organic chemical-vapor deposition

A comparison of gallium-nitride (GaN) films grown on large-area Si(111) using a single aluminum-nitride (AlN) buffer, an AlN/graded-AlxGa1−xN buffer, and the introduction of additional low-temperature (LT)-grown AlN interlayers is reported. A graded-AlGaN buffer followed by additional LT-AlN interlayers is shown to completely eliminate cracking in nitride films of thickness >2 µm and also reduce the threading-dislocation density significantly. A partial compensation of GaN-tensile strain by the compressive-lattice strain induced by the AlGaN and AlN layers is responsible for this effect. The surface roughness is increased by the introduction of the LT-AlN buffers.

MOVPE growth of GaN on Si(1 1 1) substrates

Metalorganic chemical vapor phase deposition of thick, crack-free GaN on Si can be performed either by patterning of the substrate and selective growth or by low-temperature (LT) AlN interlayers enabling very thick GaN layers. A reduction in dislocation density from 10 10 to 10 9 cm −2 is observed for LT-AlN interlayers which can be further improved using monolayer thick Si x N y in situ masking and subsequent lateral overgrowth. Crack-free AlGaN/GaN transistor structures show high room temperature mobilities of 1590 cm 2/V s at 6.7×10 12 cm −2 sheet carrier concentration. Thick crack-free light emitters have a maximum output power of 0.42 mW at 498 nm and 20 mA.

Efficient stress relief in GaN heteroepitaxy on Si(1 1 1) using low-temperature AlN interlayers

Low-temperature (LT) AlN interlayers can be applied to reduce the tensile stress and cracks in thick GaN layers on Si. Here, we present an X-ray diffractometry study revealing the influence of metalorganic chemical vapor phase deposition parameters on stress relaxation by these interlayers. The degree of stress relaxation is observed to strongly depend on interlayer deposition temperature. At low temperatures, LT-AlN grows incoherently on GaN, which leads to a temperature-dependent partial decoupling of stress and also to a decoupling of the GaN layers separated by the interlayers. We further observe a Ga incorporation into the LT-AlN interlayers dependent on growth temperature and Al-content of AlGaN layers grown on top of LT-AlN layers. By introducing LT-AlN interlayers a GaN X-ray diffractometry rocking curve FWHM of the (0 0 0 2) reflection of 400 arcsec for 3 μm thick crack-free layers is achieved.

The Role of the Multi Buffer Layer Technique on the Structural Quality of GaN

Successive growth of thick GaN layers separated by either LT-GaN or LT-AlN interlayers have been investigated by transmission electron microscopy techniques. One of the objectives of this growth method was to improve the quality of GaN layers by reducing the dislocation density at the intermediate buffer layers that act as barriers to dislocation propagation. While the use of LT-AlN results in the multiplication of dislocations in the subsequent GaN layers, the LT-GaN reduces dislocation density. Based upon Burgers vector analysis, the efficiency of the buffer layers for the propagation of the different type of dislocations is presented. LT-AlN layer favor the generation of edge dislocations, leading to a highly defective GaN layer. On the other hand, the use of LT-GaN as intermediate buffer layers appears as a promising method to obtain high quality GaN layer.

The Role of the Multi Buffer Layer Technique on the Structural Quality of GaN

AbstractSuccessive growth of thick GaN layers separated by either LT-GaN or LT-AlN interlayers have been investigated by transmission electron microscopy techniques. One of the objectives of this growth method was to improve the quality of GaN layers by reducing the dislocation density at the intermediate buffer layers that act as barriers to dislocation propagation. While the use of LT-AlN results in the multiplication of dislocations in the subsequent GaN layers, the LT-GaN reduces dislocation density. Based upon Burgers vector analysis, the efficiency of the buffer layers for the propagation of the different type of dislocations is presented. LT-AlN layer favor the generation of edge dislocations, leading to a highly defective GaN layer. On the other hand, the use of LT-GaN as intermediate buffer layers appears as a promising method to obtain high quality GaN layer.