K. Meehan

Disorder of an AlxGa1−xAs‐GaAs superlattice by donor diffusion

The Si impurity is diffused (850u2009°C, 10 h, x j ∼2.4 μm) into 2.4 μm of Al x Ga1−x As‐GaAs (x≳0.6) superlattice (barrier L B ≊320 A, quantum wellL z ≊280 A) and disorders it into bulk‐crystal Al x′Ga1‐x′As (x′≳0.32). The as‐grown infrared gap superlattice is converted selectively to red gap bulk crystal and, where undiffused and not disordered, is still capable of continuous 300‐K photopumped laser operation at a threshold of 4×103 W/cm2 (or J eq ∼1.7×103 A/cm2, 5145 A pump photon).

Implantation disordering of AlxGa1−xAs superlattices

Data are presented showing that layer disordering of Al x Ga1 − x As‐GaAs quantum wellheterostructures (QWH’s) or superlattices (SL’s) via ion implantation can be effected with a lattice constituent (Al), an inert ion (Kr), or an active impurity (Zn, Si, S, etc.). A doping impurity that diffuses (during annealing) via multiple sites, making column III sites available for Al‐Ga interchange, is most effective in layer disordering. However, any implanted ion is itself relatively effective in converting an Al x Ga1 − x As‐GaAs QWH or SL to bulk‐crystal Al y Ga1 − y As (0≤y≤x) via damage‐induced disordering.

Stripe‐geometry AlxGa1−xAs‐GaAs quantum well heterostructure lasers defined by Si diffusion and disordering

The use of Si diffusion and impurity‐induced layer disordering, via a Si3N4 mask pattern, to construct stripe‐geometry Al x Ga1−x As‐GaAs quantum wellheterostructure lasers on n‐type substrates is described. This leads to a convenient form of index‐guided buried‐heterostructure laser that is easily constructed and replicated (in various geometries) on commonly available n‐type GaAs substrate.

Transient capacitance spectroscopy on large quantum well heterostructures

We report transient capacitancemeasurements on Al x Ga1−x As–GaAs–Al x Ga1 −x As (x∼0.35) double heterojunctions with a large quantum well active region (L z ∼800 A). It is suggested that the thin GaAs layer acts as a ‘‘giant’’ artificial deep level. It follows then that the band edge discontinuity ΔE c determines the electron emission rates (from the thin layer), thus making it possible for ΔE c to be determined by transient capacitancemeasurements.

Stripe‐geometry AlGaAs‐GaAs quantum‐well heterostructure lasers defined by impurity‐induced layer disordering

Stripe‐geometry AlGaAs‐GaAs single quantum‐well heterostructure lasers are demonstrated in which the region complementary to the stripe (outside of and defining the stripe) is shifted to higher band gap, and lower refractive index, by low‐temperature (600u2009°C) Zndiffusion. Impurity‐induced Al‐Ga interdiffusion causes the single GaAsquantum well (x=0, L z ≊80 A) outside of the stripe region to be mixed (‘‘absorbed,’’ x→x′) into the Al x′Ga1−x′As (x′∼0.3, L z′≊0.18 μm) bulk‐layer waveguide of the crystal.

Impurity-disordered, coupled-stripe AlxGa1−xAs-GaAs quantum well laser

Continuous room‐temperature operation of impurity‐disordered, coupled‐stripe Al x Ga1−x As‐GaAs quantum wellheterostructure lasers is described. Silicon (donor) diffusion at 850u2009°C is used to produce layer disordering and index guiding, in addition to providing carrier confinement in a ten‐stripe coupled array (8‐μm‐wide stripes on 10‐μm centers).

Thermal-anneal wavelength modification of multiple-well p-n AlxGa1−x As-GaAs quantum-well lasers

Data are presented showing that ordinary thermal annealing can be used to modify GaAs square wells into rounded Al x Ga1−x As quantum wells and shift the continuous 300‐K laser operation of a p‐n multiple‐well Al x Ga1−x As–GaAs heterostructure laser to higher energy. Transmission electron microscopy is used to show that thermal annealing at 900u2009°C for 10‐h changes, for example, well sizes from 85 to 105 A and coupling barriers from 95 to 75 A, which results in a change of laser photon energy of Δℏω∼50 meV. Bandfilling is minimal in multiple quantum‐well lasers, thus making thermal annealing a useful method to ‘‘tune’’ a continuous 300‐K quantum‐well laser to shorter wavelength as shown here. These thermal annealing experiments indicate that the Al‐Ga interdiffusion coefficient at a heterointerface is D(900)∼10− 1 8 cm2/s.

Photoluminescence and stimulated emission in Si- and Ge-disordered AlxGa1−xAs-GaAs superlattices

Photoluminescence and absorption data are presented on Al x Ga1−x As‐GaAs superlattices(SLs) disordered into bulk‐crystal Al y Ga1−y As (0≤y≤x) by Si or Gediffusion. The bulk‐crystal Al y Ga1−y As produced by impurity‐induced disordering (by Al‐Ga interchange) 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≊0.23<y c =0.44, the direct‐indirect crossover), in absorption the Ge‐ or Si‐disordered SL exhibits (4.2 and 77 K) the bulk‐crystal exciton, which is characteristic of homogeneous alloy (Al y Ga1−y As). Stimulated emission (4.2 and 77 K) in bulk‐crystal Al y Ga1−y As is observed ΔE≤50 meV below the band edge via photopumping for both Si‐ and Ge‐disordered SLs of Al concentration yielding y∼0.23 and y∼0.39. Shallow hydrogenlike donor or acceptor states are characteristic of Al x Ga1−x As‐GaAs SLs disordered with Ge or with Si. For the Si impurity (i.e., an Al x Ga1−x As‐GaAs SL disordered with Si), however, much deeper states (transitions) are observed that saturate at higher photoexcitation levels. These states are attributed to nearest‐neighbor or extended Si‐Si pairs since similarly disordered Al x Ga1−x As‐GaAs SLs doped with Ge do not exhibit deeper states.

Donor‐induced disorder‐defined buried‐heterostructure AlxGa1−xAs‐GaAs quantum‐well lasers

A simple form of a buried heterostructure Al x Ga1−x As‐GaAs quantum‐well laser is described that is realized by impurity‐induced layer disordering (d o n o r‐i n d u c e d disordering). The layer disordering [and the resulting band‐gap shift to higher energy (and lower index)] is accomplished by Si diffusion in a stripe pattern defined by a Si3N4 mask. Single‐mode lasers of stripe width 3 and 6 μm are demonstrated that operate continuously at 300 K in the threshold current range of 10–25 mA and with single‐facet power levels as high as 10–20 mW.

Si-implanted and disordered stripe-geometry AlxGa1-xAs-GaAs quantum well lasers

The Si impurity is implanted into an Al x Ga1−x As‐GaAs quantum wellheterostructure to form, by impurity‐induced layer disordering and donor doping, a stripe‐geometry buried heterostructure laser.