P. A. Grudowski

Comprehensive characterization of metal–semiconductor–metal ultraviolet photodetectors fabricated on single-crystal GaN

We report on the material, electrical, and optical properties of metal–semiconductor–metal ultraviolet photodetectors fabricated on single-crystal GaN, with active layers of 1.5 and 4.0 μm thickness. We have modeled current transport in the 1.5 μm devices using thermionic field emission theory, and in the 4.0 μm devices using thermionic emission theory. We have obtained a good fit to the experimental data. Upon repeated field stressing of the 1.5 μm devices, there is a degradation in the current–voltage (I–V) characteristics that is trap related. We hypothesize that traps in the GaN are related to a combination of surface defects (possibly threading dislocations), and deep-level bulk states that are within a tunneling distance of the interface. A simple qualitative model is presented based on experimental results. For devices fabricated on wafers with very low background free electron concentrations, there is a characteristic “punch-through” voltage, which we attribute to the interaction of the depletion ...

Very low dark current metal–semiconductor–metal ultraviolet photodetectors fabricated on single-crystal GaN epitaxial layers

We report a very low dark current (∼57 pA at 10 V reverse bias) metal–semiconductor–metal photodetectors fabricated on GaN epitaxial layers grown by low-pressure metalorganic chemical vapor deposition. The photodetectors exhibit the typical sharp band-edge cutoff, with good responsivity. There is indication of a photoconductive gain mechanism. We also performed a Medici simulation to establish an effective area for current density calculations.

Selective-area and lateral epitaxial overgrowth of III–N materials by metal organic chemical vapor deposition

We describe the characteristics of single-crystal GaN regions obtained by selective-area and subsequent lateral epitaxial overgrowth using metal organic chemical vapor deposition. Under certain deposition conditions, the surface kinetics of the metal organic chemical vapor deposition process results in lateral growth of single-crystal GaN over the masked region. The lateral-to-vertical relative growth rate depends upon the orientation of stripe openings, the ratio of the “open” stripe width to the “masked” stripe width, and the growth conditions (e.g., temperature and V/III ratio). The specific orientations of the growth facets on the sidewalls of the laterally growing stripes are also dependent upon the growth conditions. The cathodoluminescence intensity of the GaN films indicate that improved materials are grown over the oxide mask.

Current transport mechanisms in GaN-based metal–semiconductor–metal photodetectors

We report on the current transport mechanisms dominant at the Schottky interface of metal–semiconductor–metal photodetectors fabricated on single-crystal GaN, with active layers of 1.5 and 4.0 μm thickness. We have modeled transport in the 1.5 μm devices using thermionic emission theory, and in the 4.0 μm devices using thermionic field emission theory. We have obtained a good fit to the experimental data. We hypothesize that traps in the GaN are related to a combination of surface defects (possibly threading dislocations), and deep-level bulk states that are within a tunneling distance of the interface. A simple qualitative model is presented.

Very high-speed metal-semiconductor-metal ultraviolet photodetectors fabricated on GaN

We report on the temporal and the frequency response of metal-semiconductor-metal ultraviolet photodetectors fabricated on single-crystal GaN. The best devices show a fast 10%–90% rise time of ∼23 ps implying a bandwidth of >15 GHz. These time domain data have been corroborated by direct measurement of the power spectral content. From this a cutoff frequency, f3 dB, of ∼16 GHz has been obtained. Analysis in terms of reverse bias and geometric scaling indicates that the photodetectors are transit-time limited. Modeling of the temporal behavior indicates that a slow component in the time and frequency response data is a consequence of the hole drift velocity.

The effect of substrate misorientation on the photoluminescence properties of GaN grown on sapphire by metalorganic chemical vapor deposition

We report the growth and photoluminescence (300 and 4.2 K) characterization of unintentionally doped GaN on both exact and vicinal (0001) sapphire substrates. The GaN heteroepitaxial layers are grown by metalorganic chemical vapor deposition on sapphire substrates using various growth conditions. The (0001) Al2O3 c‐plane substrates are oriented exactly (0001) or misoriented either 2° towards the a plane (1120), 5° towards the m plane (1010), or 9° toward the m plane. A comparison of the 300 and 4.2 K optical characteristics of the samples grown on the different substrates indicates that a higher photoluminescence intensity is measured for the films on misoriented substrates.

Activation studies of low-dose Si implants in gallium nitride

The implantation of Si ions into undoped high-resistivity GaN films is of interest for the realization of high-performance digital and monolithic microwave integrated circuits. We report the effect of postimplant annealing conditions on the electrical, optical, and surface morphology of Si ion-implanted GaN films. We demonstrate high activation efficiencies for low-dose Si implants into unintentionally doped GaN/sapphire heteroepitaxial films. The Si ions were implanted through an epitaxial AlN cap layer at 100 keV and a dose ∼5×1014 cm−2. Samples were subsequently annealed in an open-tube furnace for various times and temperatures. The postanneal electrical activation is correlated with the surface morphology of the film after annealing. The samples annealed at 1150 °C in N2 for 5 min. exhibited a smooth surface morphology and a sheet electron concentration ns∼6.8×1013 cm−2.

Properties of InGaN quantum-well heterostructures grown on sapphire by metalorganic chemical vapor deposition

We report the growth and characterization of InGaN heteroepitaxial thin films and quantum-well heterostructures on (0001) sapphire substrates. The III-N heteroepitaxial layers are grown by metalorganic chemical vapor deposition on sapphire substrates using various growth conditions. A comparison of the 300 K photoluminescence (PL) spectra of the samples indicates that a higher PL intensity is measured for the quantum-well structures having an intentional n-type Si-doping concentration. Furthermore, three-, five-, and eight-period InGaN quantum-well structures exhibit similar narrow PL spectra.

Selective-area and lateral epitaxial overgrowth of III-N materials by metalorganic chemical vapor deposition

Abstract We describe the characteristics of single-crystal GaN regions obtained by selective-area and subsequent lateral epitaxial overgrowth using metalorganic chemical vapor deposition. For a range of deposition conditions, the surface kinetics of the metalorganic chemical vapor deposition process results in an initial stage of selective-area growth, subsequently followed by the lateral growth of single-crystal GaN over the SiO 2 mask. The lateral-to-vertical relative growth rate depends upon the orientation of stripe openings with respect to the GaN crystal planes, the ratio of the “open” stripe width to the “masked” stripe width, and the specific growth conditions (e.g., temperature and V/III ratio). The crystalline orientations of the growth facets on the sidewalls of the laterally growing stripes are also dependent upon the growth conditions. The results of cathodoluminescence and transmission-electron microscopy studies of the GaN films indicate that materials with improved quality are grown over the oxide mask.

Optical transitions in Pr-implanted GaN

Photoluminescence (PL) spectroscopy has been used to investigate praseodymium (Pr) related transitions in Pr-implanted GaN. Wurtzite GaN epilayers were grown by metalorganic chemical vapor deposition on sapphire substrates and subsequently ion implanted with Pr to a dose of 5.7×1013/cm2. The implanted samples were annealed in nitrogen to facilitate recovery from implantation related damage. Narrow PL emission bands related to 4f intrashell transitions of the trivalent Pr ion were observed near 650, 950, 1100, and 1300 nm. The dependence of PL emission on sample temperature, excitation intensity, oxygen incorporation, and annealing temperature was systematically studied. We find that the PL efficiency increases exponentially with annealing temperature up to the maximum temperature of 1050 °C applied in the current study. Furthermore, the PL emission shows no evidence of significant thermal quenching over the sample temperature range of 10–300 K. This thermal stability will have particular advantages for ap...