W.V. Lundin

Room-temperature photopumped InGaN/GaN/AlGaN vertical-cavity surface-emitting laser

We report photopumped room-temperature surface-mode lasing at 401 nm in a InGaAlN vertical-cavity surface-emitting laser grown on a sapphire substrate using metal–organic vapor-phase epitaxy. A 2λ cavity was formed by a quarter-wave Al0.15Ga0.85N/GaN distributed Bragg reflector on the one side of the active layer and a GaN–air interface on the other. A multilayer structure composed of 12-fold-stacked ultrathin InGaN insertions in a GaN matrix served as an active layer providing ultrahigh material gain and making possible vertical lasing without use of the upper Bragg reflector.

Influence of metalorganic chemical vapor deposition growth conditions on In-rich nanoislands formation in InGaN/GaN structures

The influence of different growth conditions on the In distribution in ultrathin InGaN insertions in a GaN matrix is investigated by high-resolution transmission electron microscopy and an appropriate image evaluation technique. It is demonstrated that the indium distribution represents dense arrays of In-rich nanodomains inserted in a layer with a lower indium concentration. The sizes of the In-rich regions are about 4–5 nm at a growth temperature of 720u200a°C. Increasing the growth temperature leads to a strong decrease in the of nanoisland density and, also, a moderate decrease in their lateral size. Increasing the trimethylindium/trimethylgallium ratio strongly increases the density of the islands, but the lateral size remains weakly effected. The observations are in agreement with a thermodynamic model of island formation including entropy effects.

Formation of GaAsN nanoinsertions in a GaN matrix by metal-organic chemical vapour deposition

Coherent ultrathin GaAsN insertions are formed in a GaN matrix by predeposition of an ultrathin GaAs layer on a GaN surface, followed by annealing in an NH3 atmosphere and overgrowth with GaN. During the overgrowth, most of the As atoms are substituted by N, with a dense array of coherent GaAsN nanodomains with lateral sizes of about 3-4 nm formed in the GaN matrix. We report a green luminescence due to GaAsN insertions, surviving at high observation temperatures and excitation densities.

Photopumped InGaN/GaN/AlGaN Vertical Cavity Surface Emitting Laser Operating at Room Temperature

Room temperature operation in the wavelength range of 401 to 415 nm has been successfully realized in InGaN/GaN/AlGaN vertical cavity surface emitting lasers (VCSELs) under photoexcitation. The VCSELs are grown by metal-organic vapor phase deposition and composed of a 2l vertical cavity including twelvefold stacked multiple InGaN insertions in a GaN matrix grown on top of a quarter-wave strain-compensated Al0.15Ga0.85N/GaN distributed Bragg reflector.

A new approach to analysis of mosaic structure peculiarities of gallium nitride epilayers

Abstract The successful results of multifractal analysis application to a quantitative description of mosaic structure peculiarities, which are typical for GaN epitaxial layer with hexagonal modification grown on (0xa00xa00xa01) sapphire substrates, have been obtained. A linear dependence of mobility on the multifractal parameters of surface topology of the mosaic structure (the self-organization degree and the disruption of the local symmetry) has been observed in GaN layers.

MOSAIC STRUCTURE AND SI DOPING RELATED PECULIARITIES OF CHARGE CARRIER TRANSPORT IN III-V NITRIDES

Studies of the charge carrier transport in undoped, moderately and heavily Si doped GaN and AlxGa1—xN (x = 0.1 to 0.2) epilayers with different mosaic structure are presented. The epilayers were grown by low-pressure MOCVD on (0001) sapphire substrates. The mosaic (columnar) structure of the epilayers has been characterized by X-ray diffraction and AFM surface topography studies. Application of electrostatic force microscopy (EFM) permitted to reveal irregular potential barriers at the mosaic domain boundaries in undoped layers and their reduction in Si doped layers. For undoped GaN and AlGaN epilayers unconventional transport of electrons (dependence σ ∼ exp (—1/T)) and a low RT mobility (20 to 70 cm2 V—1 s—1) have been found. We relate the peculiarities in the electron transport in undoped samples with additional carrier scattering on the potential barriers at domain boundaries. Si doping reduces the potential barriers. Moderate Si doping causes a considerable increase of the electron RT mobility up to 600 cm2 V—1 s—1 and restores the dependence μ ∼ T3/2.

Influence of the carrier gas composition on metalorganic vapor phase epitaxy of gallium nitride

The influence of hydrogen and nitrogen as carrier gases on the rates of gallium nitride (GaN) growth and etching in the process of metalorganic vapor phase epitaxy (MOVPE) have been studied. Based on these data, the possible roles of hydrogen and nitrogen in the events on the surface of an epitaxial GaN layer are considered.

Growth of AlGaN epitaxial layers and AlGaN/GaN superlattices by metal-organic chemical vapor deposition

Special features of metal-organic chemical vapor deposition of AlGaN epitaxial layers and AlGaN/GaN superlattices either in an Epiquip VP-50 RP research and development reactor (for a single wafer 2 in. in diameter) or in an AIX2000HT production-scale reactor (for up to six wafers 2 in. in diameter) are stud-ied. It is found that the dependence of the aluminum content in the solid phase on the trimethylaluminum (TMA) flux in a reactor levels off; this effect hinders the growth of the layers with a high aluminum content in both types of reactors and is more pronounced in the larger reactor (AIX2000HT). Presumably, this effect is a consequence of spurious reactions in the vapor phase and depends on the partial pressure of TMA in the reactor. The aluminum content in the layers can be increased not only by reducing the total pressure in the reactor but also by increasing the total gas flow through the reactor and reducing the trimethylgallium flux. The approaches described above were used to grow layers with a mole fraction of AlN as large as 20% in the AIX2000HT production-scale reactor at a pressure of 400 mbar (this fraction was as large as 40% at 200 mbar). AlGaN layers with the entire range of composition were grown in the Epiquip VP-50 RP reactor.

Possible impact of surface morphology on stimulated emission in GaN–AlGaN double heterostructures

Abstract Stimulated emission is studied in a hexagonal AlGaN/GaN/AlGaN double heterostructure grown on a (0xa00xa00xa01) sapphire substrate by low pressure (200xa0mbar) metallorganic vapor phase epitaxy. A sharp increase in the edge emitted luminescence intensity is obtained above a threshold excitation density of 40xa0kW/cm2 and is accompanied by a strong narrowing of the luminescence line width. The specific surface morphology of the heterostructure is suspected to be responsible for an optical feedback in the sample. Although the surface is extremely smooth yielding roughness values of σRMS

Vapor phase epitaxy of aluminum nitride from trimethylaluminum and molecular nitrogen

We have studied the pyrolysis of trimethylaluminum (TMA) in a nitrogen-containing atmosphere of a vapor phase epitaxy reactor. It is established that, in the presence of gallium nitride coatings in the reactor, the main product of TMA pyrolysis in a nitrogen-hydrogen atmosphere is aluminum nitride. Using this process (without introducing ammonia), we obtained perfect epitaxial aluminum nitride layers.