Orientation of (100) InGaAsP/InP Wafers By HCI Chemical Etching

A wide variety of optical, electronic, and optoelectronic devices are currently being developed on InP or InP-substrate based systems, l- Many of these devices require a special orientation of the substrate to achieve the desired device structure. Injection lasers fabricated from the InGaAsP/InP material system provide one example. These are currently of interest for application in optical fiber communication systems operating at ~. = 1.3 tzm and 1.55 #m. Laser structures that utilize a real refractive index waveguide, such as the buried heterostructure (BH), channel substrate or ridge waveguide lasers, have been shown to have advantages with respect o current hreshold, output spectra, and freedom from pulsations or light jump behavior. 2 For most refractive index- guided laser structures, the fabrication sequence usually requires a chemical etching step to formeither a mesa or channel which ultimately defines the optical cavity of the laser. We find that, similar to the case of GaAs, 3 preferentially etched mesas or channels on (100) InP wafers have different side wall geometries depending on the orientation of the etching mask with respect to the [011] or [01]'] crystal directions. Fig. 1 illustrates the result with HC1 etching and mask edges aligned along either the [011] or [015] direction or, (100) InP. 4 Note that the (01]') plane is exposed for the orientation in Fig. l(a) but the corresponding (011) plane is not defined when the mask is rotated 90 * as in Fig. 1 (b). As is generally the case for III-V compounds with the zinc-blend crystal structure, the relative orientation of the polar generic {111} planes are the major contributing factors to this kind of selective tching anisotropy. 3-7 As detailed by Tuck, 5one se