Joseph M. Blum

Growth of Smooth Uniform Epitaxial Layers by Liquid‐Phase‐Epitaxial Method

The liquid‐phase‐epitaxial (LPE) process has proven to be a very effective technique for the formation of high‐quality III‐V semiconductor layers. It has found widespread use because devices made by this method produce high‐efficiency LEDs and low‐threshold lasers. A limitation of this method has been the difficulty of making smooth high‐quality surfaces. It will be shown that the use of a specially designed LPE growth apparatus makes possible the growth of reproducible uniform economical and, above all, smooth photolithographic processable layers. This process has made possible the formation of planar monolithic AlxGa1−xAs LEDs with luminance characteristics as high as 104 ft L at a current density of ∼40 A/cm2.

Deep trench plasma etching of single crystal silicon using SF6/O2 gas mixtures

A new magnetron ion etching (MIE) process has been developed to etch 50 μm deep trenches into single crystal silicon. The optimized SF6/O2 gas mixture results in a nearly vertical etch profile with a vertical to horizontal etch rate ratio of 9.4. Similar experiments were carried out on a Drytek reactive ion etching (RIE) system. Results indicate that although the sidewall angle, etch rate ratio, and etch rate of the RIE process for silicon is lower than that of the MIE process, the surfaces of the trench are smoother and more defect‐free due to better substrate cooling. The effects of the processing parameters on the silicon etch rate and anisotropy were explored in order to optimize both the MIE and RIE processes. Both processes were used to fabricate single crystal silicon doughnuts of dimensions 25–50 μm thick, 50 μm inner diameter, and 100–200 μm outer diameter.

Deposition of amorphous silicon using a tubular reactor with concentric‐electrode confinement

High‐quality, hydrogenated amorphous silicon (a‐Si:H) is deposited at room temperature by rf glow discharge at a high deposition rate using a tubular reactor with cylindrical symmetry (concentric‐electrode plasma‐enhanced chemical vapor deposition, CE‐PECVD). Using the novel CE‐PECVD design, room‐temperature deposition of a‐Si:H with growth rates up to 14 A s−1, low hydrogen concentration (≲10%), and the bonded hydrogen in the Si‐H monohydride configuration, is achieved for the first time using an rf glow‐discharge technique. The influence of the deposition parameters (silane flow rate, pressure, and power density) on the growth rate, optical band gap, and silicon‐hydrogen bonding configuration, is quantitatively predicted using a deposition mechanism based on the additive contribution of three growth precursors, SiH2, SiH3, and Si2H6, with decreasing sticking coefficients of 0.7, 0.1, and 0.001, respectively. The low hydrogen concentration is due to the enhanced ion bombardment resulting from the concent...

Annealing kinetics of a‐Si:H deposited by concentric‐electrode rf glow discharge at room temperature

The irreversible isothermal annealing of the as‐deposited defects of hydrogenated amorphous silicon, a‐Si:H, deposited at room temperature by concentric‐electrode radio‐frequency glow discharge is studied using dark and photoconductivity, space‐charge limited current, and time‐of‐flight. The photoconductivity increases as a power law of the annealing time with exponent 0.8. The density of states at the Fermi level, measured by space‐charge limited current, is inversely proportional to the annealing time. These results are compatible with bimolecular annealing kinetics. The dark conductivity obeys a Meyer–Nelder rule during the isothermal anneal.

The effect of the flow of silane on the properties of a‐Si:H deposited by concentric‐electrode radio frequency glow‐discharge

High band gap, device‐quality, hydrogenated amorphous silicon (a‐Si:H) was deposited from silane at room temperature using concentric‐electrode plasma‐enhanced chemical vapor deposition (CE‐PECVD). Increasing the flow of silane from 15 to 99 sccm resulted in a continuous increase of the optical band gap, Eopt, from 1.7 to 2.1 eV, and changed the dominant bonding configuration from Si‐H to Si‐H2. The total hydrogen concentration as determined from the integrated absorption of the SiHx stretching bond increased from 7% to 15%. As Eopt varied between 1.7 and 2.1 eV, the photoconductivity, σph, decreased from 10−5 to 10−7 Ω−1 cm−1 and the dark conductivity, σd, dropped from 10−10 to 10−14 Ω−1 cm−1 (σph and σd measured at room temperature after a 1 h anneal at 200 °C). These results are superior to those obtained using a‐SiC:H alloys deposited under comparable conditions (i.e., without hydrogen dilution). After annealing, three different conduction paths were identified and correlate with the silicon‐hydrogen ...

AlxGa1−xAs Grown‐Diffused Electroluminescent Planar Monolithic Diodes

AlxGa1−xAs p‐n junctions have been grown on p‐type GaAs substrates by the push‐pull liquid‐phase‐epitaxy method. Zn was subsequently diffused to form planar monolithic grown‐diffused p‐n junctions which produce high‐efficiency light with excellent luminance characteristics. A description will be given of the preparation and processing of the structures. The properties of the epitaxial layers and the grown‐diffused p‐n junctions will be discussed.