Donor-Induced Layer Disordering via Silicon Diffusion in Aluminum-Gallium Arsenide - Gallium-Arsenide Quantum-Well Heterostructures, and Disorder-Defined Index-Guided Stripe Geometry Laserdiodes

Abstract

The use of Si diffusion to disorder Al(,x)Ga(,1-x)As-GaAs quantum-well heterostructures (QWHs) and quantum-well (QW) p-n junction lasers is described. Under the proper diffusion conditions Si produces n-type conductivity in Al(,x)Ga(,1-x)As layers, and will counterdope (to n-type) initially p-type Al(,x)Ga(,1-x)As regions which form the top confining layer of p-n QW laser that is grown on an n-type GaAs substrate. Si diffusion is masked with a Si(,3)N(,4) layer which can be patterned using standard photolithography and plasma etching, thus producing an arbitrary pattern of Si-diffused and disordered regions adjacent to masked, as-grown crystal. The current confinement due to the Si doping, in combination with the refractive index step that results from Si-induced intermixing of Al(,x)Ga(,1-x)As-GaAs QW layers is effective in producing stripe-geometry index-guided laser diodes. Single-stripe index-guided lasers are described, with stripe widths as narrow as 6 and 3 (mu)m. These devices lase continuously at room temperature at a threshold current of 22 mA (6-(mu)m stripe) and 11 mA (3-(mu)m stripe) and operate in the lowest-order transverse mode.

A more complicated laser structure, a ten-stripe coupled array, is also described. This is fabricated by using Si diffusion in the same manner as is used for single-stripe lasers, except for a change in the mask that defines the active region, which consists of ten as-grown stripes (8 (mu)m wide) which are separated by 2-(mu)m wide Si-diffused and disordered regions. The phased array operates continuously at room temperature; the threshold current is 130 mA, and 150 mW of optical power per laser facet are obtained at a drive current of 500 mA.

Photoluminescence and absorption data are presented on Al(,x)Ga(,1-x)As-GaAs superlattices (SLs) disordered into bulk-crystal Al(,y)Ga(,1-y)As (0 (LESSTHEQ) y (LESSTHEQ) x) by Si or Ge diffusion. The bulk-crystal Al(,y)Ga(,1-y)As produced by impurity-induced disordering is determined by transmission electron microscopy, absorption measurements, and photoluminescence to be homogeneous, with an alloy composition (y) that agrees with the average Al concentration of the SL. For low enough Al concentration ( y (DBLTURN) 0.23) in absorption the Ge- or Si-disordered SL exhibits (4.2 and 77 K) the bulk-crystal exciton, which is characteristic of homogeneous alloy.