At&t Bell Laboratories

Bell Telephone Laboratories

American Telephone & Telegraph Co., At&t Bell Laboratories

Ronald J Nelson

Randall Brian Wilson

Paul R Besomi

Barry Irwin Miller

Adam Heller

Harry John Leamy

Phillip D Wright

Bruce A Parkinson

In the fabrication of buried heterostructure InP/InGaAsP lasers, mask undercutting during the mesa etching step is alleviated by a combination of steps which includes the epitaxial growth of a large bandgap InGaAsP cap layer (1.05 eV.ltorsim.E.sub.g .ltorsim.1.24 eV) and the plasma deposition of a SiO.sub.2 etch masking layer. Alternatively, the cap layer may be a bilayer: an InGaAs layer or narrow bandgap InGaAsP (E.sub.g .ltorsim.1.05 eV), which has low contact resistance, and a thin InP protective layer which reduces undercutting and which is removed after LPE regrowth is complete. In both cases, etching at a low temperature with agitation has been found advantageous.

Buried heterostructure devices with unique contact-facilitating layers

Thermal degradation of compound single crystal substrates (e.g., InP) containing a relatively volatile element (e.g., P) prior to LPE growth has been virtually eliminated by an improved protection technique. A partial pressure of the volatile element is provided by a solution (e.g., Sn-In-P) localized inside a chamber which is external to the LPE boat and which surrounds substrate prior to growth, thereby preventing thermal damage to the substrate surface. Applicability of the technique to other epitaxial growth processes (e.g., VPE and MBE) is also discussed.

Protection of semiconductor substrates during epitaxial growth processes

Elimination of mask undercutting in the fabrication of InP/InGaAsP BH

Discrete InP-InGaAsP mesa double heterostructure lasers have been fabricated by a batch process in which the laser mirrors are formed by chemically etching the wafer from the top surface down into the substrate. A feature of the process is that the metal contact on the top surface is recessed within the periphery of an overlying mask, and the etching time is controlled so that the contact is not undercut by the sidewalls of the mesa. Another feature is the use of a self-limiting etchant which etches the mirrors smoothly and at a faster rate than the sidewalls. Preferably, the mirrors etch isotropically and the sidewalls etch preferentially along crystallographic planes. Also described is subsequent batch processing (e.g., forming mirror coatings) and on-wafer testing of the etched-mirror lasers.

Batch processing of semiconductor devices

Semiconductor devices using chemically treated n-type GaAs have greatly reduced surface recombination velocities. A preferred embodiment uses fractional monolayers of ruthenium on the GaAs surface.

Gallium arsenide devices having reduced surface recombination velocity

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Berkeley Heights, NJ, United States of America

Ronald J Nelson