D. A. Stocker

Crystallographic wet chemical etching of GaN

We demonstrate well-controlled crystallographic etching of wurtzite GaN grown on c-plane sapphire using H3PO4, molten KOH, KOH dissolved in ethylene glycol, and NaOH dissolved in ethylene glycol between 90 and 180 °C, with etch rates as high as 3.2 μm/min. The crystallographic GaN etch planes are {0001}, {1010}, {101 1}, {101 2}, and {1013}. The vertical {1010} planes appear perfectly smooth when viewed with a field-effect scanning electron microscope. The activation energy is 21 kcal/mol, indicative of reaction-rate limited etching.

Microcavity effects in GaN epitaxial films and in Ag/GaN/sapphire structures

Luminescence spectra of GaN epitaxial layers grown on sapphire display a strong intensity modulation of the below-band gap transitions and on the low-energy side of the near-band gap transition. The intensity modulation is attributed to a microcavity formed by the semiconductor–air and semiconductor–substrate interface. The microcavity effect is enhanced by using metallic reflectors which increase the cavity finesse. It is shown that microcavity effects can be used to determine the refractive index of the microcavity active material. Using this method, the GaN refractive index is determined and expressed analytically by a Sellmeir fit.

Yellow luminescence depth profiling on GaN epifilms using reactive ion etching

Depth profiling measurements of photoluminescence on GaN epitaxial films grown on c-plane sapphire with metalorganic chemical vapor deposition have been performed. Dry etching technique of reactive ion etching is used with reactive gas of CCl2F2/H2/Ar under an operation power of 200 W. Before and after each etching, reflectivity and photoluminescence spectra are measured. Film thickness is determined from both the scanning electron microscopy and the interference oscillations of the reflectivity spectra. An excellent steady etching rate of 19.2 nm/min is established. The photoluminescence measurements show that both the near-band-edge and the yellow luminescence remain fairly constant until the film thickness of about 700 nm, and a large drop is obtained in the ratio of near-band-edge to yellow emission intensity under about 300 nm. Analysis shows that the yellow luminescence emitters are mostly confined within the near interface region, and supports the origin of yellow luminescence to be due to native d...

Facet roughness analysis for InGaN/GaN lasers with cleaved facets

0) 2 , where n is the refractive index of the semiconductor and l 0 is the emission wavelength. Laser emission from the optically pumped cavities shows a TE/TM ratio of 100, an increase in differential quantum efficiency by a factor of 34 above threshold, and an emission line narrowing to 13.5 meV.

Crystallographic Wet Chemical Etching of p‐Type GaN

We demonstrate crystallographic wet chemical etching of p-type GaN with etch rates as high as 1.2 μm/min. Etchants used include molten KOH, KOH dissolved in ethylene glycol, aqueous tetraethylammonium hydroxide, and phosphoric acid (H 3 PO 4 ), at temperatures ranging from 90 to 260°C, The observed crystallographic p-GaN etch planes are (0001), (1010), and (1012). The etch rates follow an Arrhenius characteristic with activation energies varying from 21 kcal/mol for KOH-based solutions to 33 kcal/mol for H 3 PO 4 . The etch rate and crystallographic nature for the various etching solutions are independent of conductivity, as shown by seamless etching of a p-GaN/undoped, high-resistivity GaN homojunction and by comparison of the etch rates of p-GaN with n-GaN.

Optically pumped InGaN/GaN lasers with wet-etched facets

Optically pumped laser action is demonstrated in InGaN/GaN double heterostructure lasers with wet-etched facets. The facets are formed by a two-step etching process which creates vertical facets with less than 5 nm roughness. The first step, photoenhanced electrochemical wet etching, is used to define the laser cavities. The second step reduces the facet roughness by crystallographic wet chemical etching. Lasing is demonstrated by an increase in the differential quantum efficiency, linewidth narrowing, and strongly polarized output above threshold. The threshold varies with cavity length from 2.4 MW/cm2 for 500 μm cavities to 23 MW/cm2 for 50 μm cavities. A modal loss of 15 cm−1 is deduced from an analysis of the threshold pumping power as a function of cavity length.

Fabrication of Smooth GaN-Based Laser Facets

A method is presented for fabricating fully wet-etched InGaN/GaN laser cavities using photoenhanced electrochemical wet etching followed by crystallographic wet etching. Crystallographic wet chemical etching of n- and p-type GaN grown on c-plane sapphire is achieved using H 3 PO 4 and various hydroxides, with etch rates as high as 3.2 μm/min. The crystallographic GaN etch planes are {0001}, {10 1 0}, {10 1 1 }, {10 1 2 }, and {10 1 3}. The vertical {10 1 0} planes appear perfectly smooth when viewed with a field-effect scanning electron microscope (FESEM), indicating a surface roughness less than 5 nm, suitable for laser facets. The etch rate and crystallographic nature for the various etching solutions are independent of conductivity, as shown by seamless etching of a p-GaN/undoped, high-resistivity GaN homojunction.

InGaN/GaN double heterostructure laser with cleaved facets

Laser action is demonstrated in InGaN/GaN double heterostructures with cleaved facets. Hydride vapor phase epitaxy is used to grow a 10-micrometer-thick buffer layer of GaN on (0001) sapphire, and metal-organic vapor phase epitaxy is used to subsequently grow a GaN/In0.09Ga0.91N/GaN double heterostructure. One-mm-long cavities are produced by cleaving the structure along the (1010) plane of the sapphire substrate. A pulsed Nitrogen laser is used for optical excitation. At room temperature, the laser threshold occurs at an incident power density of 1.3 MW/cm2. Above threshold, the differential quantum efficiency increases by a factor of 34, the emission linewidth decreases to 13.5 meV, and the output becomes highly TE polarized.