Passivation of GaAs Laser Mirrors by Ion-Beam Deposited Al 2 O 3
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PASSIVATION OF GaAs LASER MIRRORS BY ION-BEAM DEPOSITED A12 0 3 D.J. WEBB, H.-P. DIETRICH, F. GFELLER, A. MOSER, AND P. VETTIGER IBM Research Division, Zurich Research Laboratory, 8803 R~ischlikon, Switzerland ABSTRACT The use of ion-beam semiconductor injection lasers protection against corrosion, surface. The overall quality of testing of the lasers.
sputtered A12 0 3 to passivate the mirrors of is described. Dense films, which offer considerable can be deposited without damage to the crystal the passivation is demonstrated by long-term stress
INTRODUCTION The mirrors of semiconductor injection lasers [1] are usually made by cleaving the crystal on which the laser structures are fabricated. The cleaved crystal facets have a reflectivity of about 30% and initially have excellent characteristics. Such mirrors however will degrade during operation of the laser unless they are protected. Degradation occurs not only through oxidation [2] but also through non-radiative recombination at surface states [3]. This recombination can deposit a large amount of energy into the crystal. This energy causes heating which at high optical power may destroy the mirror (catastrophic optical mirror damage or COMD). At lower powers this can accelerate degradation through either corrosion or by recombination-enhanced defect reactions [4]. Laser mirrors are usually passivated by coating them with an inert, transparent, electrically insulating material. It is important that this material be compact and that the semiconductor/coating interface have as low a recombination velocity as possible. Various materials and deposition methods have been investigated (see for example [5] for a review) and A12 0 3 has gained general acceptance. Ion-beam sputter deposition has been shown to be an excellent method of producing optical coatings [6]; however, little has been published on its use for laser passivation. This paper investigates not only the optical quality of A120 3 deposited by this method, but also the electrical quality of the coating/substrate interface. DEPOSITION SYSTEM, PROCESS AND FILM PROPERTIES The ion-beam deposition equipment is shown in Figure 1. A Kaufmann-type 3-cm-diameter ion-source emits a beam of Ar ions in the energy range 300-1000 eV. This sputters material from an A12 0 3 target onto the sample. Oxygen is bled into the system during deposition, the partial pressure being 2 x 10-5 mbar. Laser bars are clamped into a holder, p-contact to n-contact, and deposition takes place at a slight angle to the facet normal to avoid shadowing. The films are deposited at room temperature without additional ion bombardment.
Mat. Res. Soc. Symp. Proc. Vol. 128. c 1989 Materials Research Society
508
Deposition System Substrate
Ar+ ,,
'Ole-
2
Figure 1. Ion-beam deposition system The pressure in the system before deposition is about 5 x 10-8 mbar and during deposition it is 4 x 10-4 mbar. Figure 2 shows the optical transmittance of films of A12 0 3 deposited on glass substrates, compared with the transmittance of the substrates al
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