InGaN GaN Research Articles

Optical and structural properties of GaN materials and structures grown on Si by metalorganic chemical vapor deposition

GaN thin films, undoped, Si- and Mg-doped, and InGaN–GaN multiple quantum well (MQW) structures have been grown on Si (001) substrates with specially designed composite intermediate layers consisting of an ultra-thin amorphous Si layer and a GaN/AlGaN multilayered buffer by low pressure metalorganic chemical vapor deposition. Their optical and structural properties were studied by a variety of characterization techniques, including X-ray diffraction (XRD), Raman scattering, Fourier transform infrared reflectance, photoluminescence, scanning and transmission electron microscopy. Wurtzite GaN structure with the single crystalline grain size up to ∼2 μm is confirmed, and material properties are improved by adjusting the growth conditions and buffer layer structural design.

Phase separation in Zn-doped InGaN grown by metalorganic chemical vapor deposition

Zn-doped InGaN thin films were deposited on GaN/sapphire by metalorganic chemical vapor deposition, and studied by a combination of high-resolution X-ray diffraction (HR-XRD), micro-photoluminescence (PL) and secondary ion mass spectrometry (SIMS). Indium phase separation is studied comparatively. HR-XRD exhibits a GaN band and a single band from InGaN for samples without phase separation, but two InGaN bands corresponding to different x(In) for samples with phase separation. PL excitation power dependence measurements reveal 2 sets of InGaN PL emissions for samples with phase separation, but only 1 set for samples without phase separation. SIMS data showed that phase separated InGaN:Zn films possess a high Zn concentration near the InGaN–GaN interface and non-uniform distributions of In and Zn contents, which are in contrast with data from InGaN:Zn films with no In-phase separation.

Study of GaN-based Laser Diodes in Near Ultraviolet Region

Ultraviolet (UV) laser diodes (LDs) were grown on epitaxially laterally overgrown GaN substrates by a metalorganic chemical vapor deposition method. We fabricated three types of UV LDs whose active layers were (I) ternary InGaN, (II) quaternary AlInGaN and (III) binary GaN single quantum well (SQW) structures. We investigated the LD characteristics in detail in the near UV region. LDs whose active layers were quaternary Al0.03In0.02Ga0.95N were demonstrated under the pulsed-current-biased conditions at room temperature. The emission wavelength of these LDs was the shortest wavelength (366.4 nm) in our experiments. We also demonstrated binary GaN SQW LDs for the first time. The threshold current density, voltage and emission wavelength of these LDs under 25°C continuous-wave (cw) operation were 3.5 kA/cm2, 4.6 V and 369.0 nm, respectively. The estimated lifetime was approximately 2000 h under 25°C cw operation at an output power of 2 mW.

Effects of piezoelectric field, bias and indium fluctuations on a InGaN–GaN single quantum well system

A drift-diffusion model and a self-consistent solution of Poisson and Schrödinger equations have been used to obtain the band profile, the energy levels and the wave functions of an InGaN quantum well. The piezoelectric field has been shown to influence the emission energy. Published experimental results match our calculations on bias dependency. However, discrepancies between the magnitude of the calculated and measured average fields in the well are found. We show that indium fluctuations affect the field inside the well and the emission energy.

High Current Gains Obtained by InGaN/GaN Double Heterojunction Bipolar Transistors

InGaN/GaN double heterojunction bipolar Npn transistors have been fabricated using p-type InGaN and n-type GaN as base and collector layers, respectively. The structures were grown on SiC substrates by low-pressure metalorganic vapor phase epitaxy. The In mole fraction in the base layer and its thickness were 0.06 and 100 nm, respectively. The Mg doping concentration in the base layer was 1 × 1019 cm—3 corresponding to a hole concentration of 5 × 1018 cm—3 at room temperature. The common-emitter I–V characteristics showed good saturation characteristics and a maximum current gain of 20 was obtained at room temperature.

High Current Gains Obtained by InGaN/GaN Double Heterojunction Bipolar Transistors

InGaN/GaN double heterojunction bipolar Npn transistors have been fabricated using p-type InGaN and n-type GaN as base and collector layers, respectively. The structures were grown on SiC substrates by low-pressure metalorganic vapor phase epitaxy. The In mole fraction in the base layer and its thickness were 0.06 and 100 nm, respectively. The Mg doping concentration in the base layer was 1 x 10 19 cm -3 corresponding to a hole concentration of 5 x 10 18 cm -3 at room temperature. The common-emitter I-V characteristics showed good saturation characteristics and a maximum current gain of 20 was obtained at room temperature.

Selective area deposited blue GaN–InGaN multiple-quantum well light emitting diodes over silicon substrates

We report on fabrication and characterization of blue GaN–InGaN multi-quantum well (MQW) light-emitting diodes (LEDs) over (111) silicon substrates. Device epilayers were fabricated using unique combination of molecular beam epitaxy and low-pressure metalorganic chemical vapor deposition growth procedure in selective areas defined by openings in a SiO2 mask over the substrates. This selective area deposition procedure in principle can produce multicolor devices using a very simple fabrication procedure. The LEDs had a peak emission wavelength of 465 nm with a full width at half maximum of 40 nm. We also present the spectral emission data with the diodes operating up to 250 °C. The peak emission wavelengths are measured as a function of both dc and pulse bias current and plate temperature to estimate the thermal impedance.

Laser-induced molecular beam epitaxy of group-III nitrides

nitrides by laser-induced molecular beam epitaxy (LIMBE). The requirements for the formation of high-quality, monocrystalline layers are much stronger than those for polycrystalline films. We have modified and improved the conventional pulsed laser deposition. In our process, we use metallic targets in a nitrogen environment instead of ceramic or pressed powder nitrides and we employ picosecond laser pulses with high energy (>1 mJ) and high repetition rate (2 kHz). We have grown GaN, AlN, InN, InGaN and Mg-doped GaN on sapphire (0001).

Quantum shift of band-edge stimulated emission in InGaN–GaN multiple quantum well light-emitting diodes

We report on the band-edge stimulated emission in InGaN–GaN multiple quantum well light-emitting diodes with varying widths and barrier thicknesses of the quantum wells. In these devices, we observe that the stimulated emission peak wavelength shifts to shorter values with decreasing well thickness. From the comparison of the results of the quantum mechanical calculations of the subbands energies with the measured data, we estimate the effective conduction- and valence-band discontinuities at the GaN–In0.13Ga0.87N heterointerface to be approximately 130–155 and 245–220 meV, respectively. We also discuss the effect of stress on the estimated values of band discontinuities.

Blue and green electroluminescence from heterostructures

Abstract GaN InGaN pn-junctions were grown by molecular beam epitaxy. Depending on the In content bright blue (470 nm) or green (513 nm) electroluminescence was observed at room temperature.

Microdisk laser structures formed in III–V nitride epilayers

Several kinds of nitride-based micro-resonators have been fabricated. Firstly, a microdisk laser structure comprising three InGaN GaN quantum wells on a thick AlN buffer has been grown by metal-organic molecular beam epitaxy and fabricated using a combination of non-selective Cl 2/CH 4/H 2/Ar dry etching and selective KOH-based wet etching of the AlN. These structures are of potential use in short wavelength photonic or optoelectronic circuits. In a second structure Er was implanted into a GaN layer to produce strong emission at 1.54 μm. Similar results have been obtained in Er-implanted AlN, and AlN doped during epitaxial growth.

Cleaved cavity optically pumped InGaN–GaN laser grown on spinel substrates

We report an optically pumped multiple-quantum-well laser of InGaN–GaN grown on cubic, (111)-oriented spinel substrates. The laser cavity is formed by cleaving. Atomic force microscopy shows that the cleaved GaN and spinel facets are of similar flatness. The onset of lasing is clearly demonstrated by the saturation of spontaneous emission, abrupt line narrowing, and the highly polarized light output. A lasing threshold power of 140 kW/cm2 is measured in a 400-μm-long cavity at 150 K.

Photoluminescence study of high quality InGaN–GaN single heterojunctions

In this letter we report the results of room-temperature continuous wave and pulsed photoluminescence measurements on InGaN–GaN single heterojunctions. These InGaN–GaN heterojunctions were deposited over basal plane sapphire substrates using low pressure metalorganic chemical vapor deposition. We suggest the use of vertical cavity stimulated emission instead of spontaneous emission peak position as a good measure of the InGaN band edge.