W. B. Joyce

Analytic approximations for the Fermi energy of an ideal Fermi gas

An important function in semiconductor‐device analysis and transport theory is the widely tabulated Fermi‐Dirac integral, F (η) =2π−1/2F∞0[exp(x−η)+1]−1f dx, f=x1/2, which relates, for example, the Fermi energy ηkT to the carrier density N=FN0 in a parabolic semiconductor band (N0=effective density of states). We show that the classical or Boltzmann approximation to this integral (η=lnF, η≲−2) is extended to cover the Fermi‐energy range of semiconductor lasers (η≲+2) by the expression η=lnF+2−3/2F and by other simple differentiable approximations applicable to higher degeneracy (η≲7) or to nonparabolic bands (f≠x1/2).

Current‐crowded carrier confinement in double‐heterostructure lasers

The profiles (spatial distributions) of injected carriers and current within a double‐heterostructure stripe‐geometry laser are described theoretically in a one‐dimensional‐flow model. The one‐dimensional model is solved exactly and found to yield comparatively simple analytical expresions even when both radiative (nonlinear) and nonradiative recombination are operative. In the case of a shallow proton bombardment or an oxide stripe, two coupled current components leak from under the stripe—an Ohmic current in the P layer and a diffusion current in the active region. As an example, these wasted leakage currents are evaluated in detail and seen to depend strongly upon the laser design. Features of this work not present in previous analytical studies include incorporation of radiative recombination (Bn2) and a carrier‐concentration‐dependent diffusion coefficient, as well as development of a self‐consistent solution for the two current components.

Statistical characterization of the lifetimes of continuously operated (Al,Ga)As double‐heterostructure lasers

The statistical distribution of lifetimes of routinely grown and fabricated continuously operated (Al,Ga)As double‐heterostructure lasers is presented and discussed. The 90 typical devices studied were operated as lasers in a dry‐nitrogen elevated‐temperature ambient (70 °C) until failure. The resulting median life, τm=750 h, and mean life, 〈τ〉=1370 h, extrapolate to τm=5.7 years and 〈τ〉=10.5 years at room temperature (22 °C) using a 0.7‐eV activation energy. The observed lifetimes are consistent with a model in which 17% of the lasers die prematurely as infant mortalities while 83% die by a mechanism well characterized by a lognormal distribution. The value of the standard deviation (σ=1.1) in lnτ is typical of other semiconductor devices.

Electrical derivative characteristics of InGaAsP buried heterostructure lasers

Results of a study of the electrical derivative characteristics of InGaAsP buried heterostructure lasers are presented. By considering current‐leakage paths and electrical contact nonlinearities, an equivalent circuit model appropriate to the buried heterostructure laser has been developed. Solutions for the theoretical electrical derivatives of series‐parallel‐reducible networks have been obtained and applied to the equivalent circuit model of the buried heterostructure laser. Comparison of experimentally measured and calculated electrical derivative characteristics provides both qualitative and quantitative information concerning the distribution of current and voltage in buried heterostructure lasers. By combining the techniques of electrical‐derivative measurement and equivalent‐circuit modelling, an improved understanding of the properties of buried heterostructure lasers has been established.

Carrier transport in double-heterostructure active layers

Use of the diffusion equation (with an effective coefficient De) for describing carrier diffusion and drift parallel to the junction in the active layer of a semiconductor double‐heterostructure is justified under commonly encountered conditions, and the effective De is evaluated. This equation is basic to the description of any laser or light emitting diode phenomenon where the injected carrier density is nonuniform. UFoff

Generalized expressions for the turn-on delay in semiconductor lasers

In semiconductor injection lasers the time delay between the application of a step function in current and the onset of lasing is widely used to extract the carrier lifetime. In this paper the common analysis of this effect is generalized to include the case in which radiative recombination significantly modifies the time delay. Expressions appropriate when a dc prebias is applied are included. Previously untreated ambiguities of interpretation of experimental data are discussed, and the possibility is suggested that time‐delay measurements can be used to separately extract the radiative and nonradiative contributions to the lifetime.

Analytic approximations for the Fermi energy in (Al,Ga)As

Simple analytic procedures are given for finding the Fermi energy in a semiconductor with a parabolic or nonparabolic band structure, and (Al,Ga)As is treated as an example of a nonparabolic material in which each of the three conduction bands, Γ, L, and X, competes effectively for electrons. The electron and hole Fermi energies form the basis for determining the voltage and further electrical characteristics of a semiconductor device.

Organizations of unsuccessful R&D projects

This paper discusses the organization and the criterion for funding of an applied research project that can be regarded as a collection of necessary but potentially unsuccessful tasks. Each task might be successfully achieved by any of a number of alternative approaches. Each alternative approach can be regarded as a collection of necessary but potentially unsuccessful subtasks. Each subtask consists of subalternatives, etc. A comparatively simple procedure is given for selecting which projects to fund, for estimating various expected expenditures, and for determining that order of carrying out the tasks, alternatives, subtasks, etc., of a project that minimizes the projects expected cost. The procedure takes into account the possibility that the project may fail and be abandoned before all tasks, subtasks, etc., are performed and the possibility that engineering considerations may exclude some economically desirable task orderings. A number of industrial practices are discussed from this viewpoint.

On the relationship of light‐output nonlinearities and light‐output spikes in proton‐bombarded stripe‐geometry double‐heterostructure (Al,Ga)As lasers

By using a fast photodetector and a simple spatial filtering technique, the relationship between the optical spike which frequently appears at the leading edge of a pulsed‐GaAs‐laser response and the optical nonlinearities called kinks has been investigated. It is suggested that the spike can be viewed consistently as a transition period during which the lasing mode distortion, which has been previously associated with kinks, occurs. It is the time taken for the kink to become established. During the spike, light emisson occurs with a spatial and angular intensity distribution consistent with the lasing which would be appropriate if the kink did not exist. It is shown that the experimental technique can also be used to investigate sustained laser optical‐intensity oscillations (pulsations).

Improved heterostructure‐laser light‐output linearity by antireflective coating

An antireflective coating is shown to raise the kink (abrupt nonlinearity in the light‐current relation) in (Al,Ga)As laser output by a factor of at least 2 or 3 in optical power before an appreciable increase in threshold current is incurred. This observation is consistent with the assumption that the kink occurs at a given optical power within the laser rather than at a given emitted power.