D. R. Scifres

AlxGa1−xAs1−y′P y′–GaAs1−yPy HETEROSTRUCTURE LASER AND LAMP JUNCTIONS

A method is described to grow successfully from solution AlxGa1−xAs1−y′P y′ (p‐type) on GaAs1−yPy (n‐type), to preserve the lattice match (y′ ≈ y), and to obtain the improved heterostructure junction devices previously realized only in the AlGaAs/GaAs system. Although not optimized, these structures have been operated as pulsed room‐temperature lasers, and because of an inherent wide‐gap window can be used conveniently for optical purposes and for excess carrier lifetime measurements. Carrier lifetime measurements, for example, indicate freedom from defects at the AlGaAsP/GaAsP barrier.

SPECTRAL BEHAVIOR, CARRIER LIFETIME, AND PULSED AND cw LASER OPERATION (77 °K) OF In1−xGaxP

The spontaneous and laser spectral behavior of high‐quality In1−x Gax P grown slowly from an In solution in a small temperature gradient is described. The band‐to‐band carrier decay times are measured below (2.3 nsec, 77°K) and above (0.85 nsec) laser threshold by an optical phase shift technique and indicate low bulk and surface losses (s≤104 cm/sec). Continuous laser operation of a thin In1−x Gax P sample is demonstrated at a photoexcitation level of ∼103 W/cm2 (hνpump =1.96 eV).

In1−xGaxP p‐n Junction Lasers

The laser operation of In1−xGaxP (x∼0.27) p‐n junctions is demonstrated at 4.2 and 77°K. The n‐type material for the junctions is grown at a fixed temperature (900–950°C) from an In solution with the InP and GaP source crystal introduced into the solution at slightly higher temperature. The p‐n junctions are formed at 700°C by Zn diffusion from an In + 10% Zn source. In comparison with InP, the threshold currents for In1−xGaxP junctions are large, which is attributed to the problems associated with introducing Zn into the In–Ga sublattice.

Double Heterojunction AlGaAsP Quaternary Lasers

Stimulated emission in AlGaAsP is demonstrated. Double heterojunction AlGaAsP lasers grown from Ga solution on GaAsP substrates exhibit 300 °K thresholds as low as 104 A/cm2 (∼ 8450 A) and shift ∼ 450 A to shorter wavelength at 77 °K. In spite of its more complicated crystalline structure, solution‐grown AlGaAsP appears to exceed in quality vapor‐grown GaAsP.

STIMULATED EMISSION IN In1 ‐xGaxP

By a modified Bridgman solution‐growth technique employing a small temperature gradient. InP and GaP source crystal are used to saturate an In solution at ∼ 925°C and grow In1−xGaxP (x ∼ 0.3) at ∼ 925°C. This material is shown to exhibit stimulated emission.

Stimulated Emission Involving the Nitrogen Isoelectronic Trap in GaAs1−xPx

Earlier work on III–V semiconductor lasers has shown that stimulated emission occurs on band‐to‐band transitions or via transitions involving donors or acceptors. Based on the behavior of the N isoelectronic trap in promoting efficient carrier recombination in GaP, the present work shows that the N isoelectronic trap in GaAs1−xPx is distinct and over part of the composition range x it can be operated in recombination in the stimulated emission (laser) regime, thus establishing a fundamental new laser transition in a III−V semiconductor. These results (4.2 and 77°K) are obtained by means of optical pumping of lightly doped n‐type samples of estimated high nitrogen concentration.

Optical phase shift measurement (77°K) of carrier decay time in direct GaAsP☆

Abstract Measurements are made (77°K) of excess carrier lifetimes and the spectral behaviour of optically excited high quality vapor grown n-type GaAs1-xPx (0.0667 ⩽ x ⩽ 0.35) for both the low level spontaneous and the high level laser regimes of excitation. In several platelet samples the ambiguities in bulk lifetime measurements resulting from surface recombination are minimized by two methods, one involving excitation through a GaAlAsP window and the other a phosphorus anneal of the sample. The spontaneous lifetime of n-type GaAsP with reduced non-radiative surface losses is typically 1–1.6 nsec which may be compared to spontaneous lifetimes of 4–5nsec (Δn ∼ 1016/cm3) for lightly doped n-type GaAs. This indicates that additional bulk non-radiative processes occur in the ternary probably arising from the disorder and strain in the alloy system.

Stimulated Emission in an Indirect Semiconductor: N Isoelectronic Trap‐Assisted Recombination in GaAs1−xPx (x > 0.44)

Due to the short‐range nature of the N isoelectronic trap potential in GaAs1−xPx and the favorable band structure of this III–V compound, strong recombination radiation can be excited on either side of the direct‐indirect transition (x=0.44, 77°K). By means of cw excitation with an argon‐ion laser, stimulated emission is demonstrated at 77°K in N‐doped indirect GaAs1−xPx (x=0.50) operating on NN pair recombination transitions.

Optically Pumped In1−xGax P Platelet Lasers from the Infrared to the Yellow (8900−5800 Å, 77°K)

The laser operation (77°K) of optically pumped thin platelets of In1−xGaxP over the composition range x=0–0.59 (8900−5800°A) is demonstrated. The samples are prepared from material grown at constant temperature (900–1000°C) from In solution with source InP and GaP introduced at slightly higher temperature. The dependence of the laser photon energy upon composition agrees well with the Γ−χ curves of Lorenz and Onton and confirms the belief that the direct‐indirect transition is at x∼0.74. In addition, unique spectral data on In1−x Gax P (x=0.27) are presented that show the mode development from spontaneous to high‐level stimulated emission.

In1−x Gax P:N Laser Operation (cw, 77°K) on the Nitrogen A‐Line Transition in Indirect Crystals (x ≥ 0.74) and in Direct Crystals above the Fundamental Band Edge (x ≥ 0.71)

The laser operation (cw, 77°K) of In1−xGaxP on the nitrogen A‐line transition in indirect crystals (x≥0.74) and in direct crystals above the fundamental band edge (x≤0.71) is reported (5450 and 5470 A, respectively). Thin (1–5 μ) experimental samples are prepared from crystals grown from In solution by a modified Bridgman method. The crystals are doped with GaN or N from the quartz of the synthesis ampoule. The samples are mounted in a sandwich configuration with indium wetted onto a copper heat sink on one side and thin CdS (10–20 μ) and sapphire on the other side. The thin samples are volume excited in a tiny spot by an argon‐ion laser focused through the sapphire window and the CdS spacer which, with the sample, forms a high‐Q compound cavity.