D. Kasemset

Pb 1-x Sn x Te/PbTe 1-y Se y lattice-matched buried heterostructure lasers with CW Single mode output

The first successful realization of buried heterostructure diode lasers in the PbSnTe/PbTeSe system is reported. This has resulted in routine cw operation above 80 K with threshold currents as low as 60 mA in 5 µm wide stripe lasers. CW operation has been achieved to 120K. In addition, these lasers operate in the fundamental transverse mode up to as much as four times threshold.

Measurement of interface recombination velocity in (Pb,Sn)Te/PbTe double‐heterostructure laser diodes

The effective minority‐carrier lifetime in the active region of Pb0.86Sn0.14Te/PbTe double‐heterostructure (DH) laser diodes has been experimentally determined for a series of diodes with active‐region widths ranging from 0.7 to 3.9 μm using a measurement technique which involves observing the dependence of the threshold current density on the duration of a current pulse input. From the data, it is inferred that the interface recombination velocity at the heterojunctions is as high as 1×105 cm/sec at 5 °K, while the bulk minority‐carrier lifetime is 4.3 nsec. For a typical double‐heterostructure laser with a 2‐μm active‐region width, this implies a reduction in the internal quantum efficiency due to interface recombination of as much as 80%.

Liquid phase epitaxy of pbtese lattice-matched to pbsnte

The conditions for liquid phase epitaxial growth of lead telluride selenide on lead tin telluride are presented, and some physical and electrical properties of the epilayers grown are described. The composition and energy gap of the quaternary lead salt compound, lead tin telluride selenide, lattice-matched to lead selenide and to lead-tin telluiride, as determined from published data, is also presented. The growth of PbSnTeSe on PbSnTe is demonstrated.

Impact ionization in Ga 1-x Al x Sb: An alternative interpretation

The existence of the recently proposed resonance impact ionization process in gallium aluminum antimonide is questioned. An alternative interpretation of the data originally used to support the claim for a resonant process is presented which invokes only conventional, well-established processes.

Longitudinal mode behavior of PbSnTe buried heterostructure lasers

Output spectra for narrow stripe, PbSnTe buried heterostructure laser diodes are presented and it is shown that the lasers operate in a single longitudinal mode of the fundamental transverse mode family to approximately twice threshold after which multimode operation predominates. These observations are interpreted in terms of the spectral inhomogeneity of the gain function. The small inhomogeneity arises from an intraband relaxation time of the order of 2 ps.

Minority carrier lifetimes and lasing thresholds of PbSnTe heterostructure lasers

A new calculation of radiative minority carrier lifetime in PbSnTe is presented which yields lifetimes an order of magnitude greater than previously accepted values. These results are used in combination with recent measurements of minority carrier lifetime and interface recombination velocity in PbSnTe double heterojunction laser structures to calculate DH laser thresholds. It is demonstrated that radiative recombination is a relatively inefficient process in present PbSnTe lasers, and that when this inefficiency is taken into account the magnitude of the experimentally observed threshold and its variation with active region width and temperature can be accurately predicted, even at low temperatures where all previous models have failed.

Reduction of interface recombination velocity with decreasing lattice‐parameter mismatch in PbSnTe heterojunctions

We report the first measurements demonstrating and quantifying the systematic reduction of the interface recombination velocity at the (Pb,Sn)Te/PbTe heterojunction interface with decreasing lattice‐parameter mismatch. The relation between the degree of lattice‐parameter mismatch and the interface recombination velocity is found to be sv = (2.9±0.3) ×107Δe/e cm/sec. In conjunction with these measurements, we have also observed very low threshold current densities in laser devices fabricated with a small degree of lattice‐parameter mimismatch. The lowest threshold current density observed was 15 A/cm2 in a Pb0.96Sn0.04Te/PbTe single‐heterostructure laser with a 20‐μm active‐region width. This is the lowest current density ever reported in (Pb,Sn)Te‐diode lasers.

AlGaAs/GaAs double‐heterojunction high electron mobility transistors grown by low‐pressure organometallic vapor phase epitaxy

AlGaAs/GaAs double‐heterojunction high electron mobility transistors (DHHEMTs) grown by low‐pressure organometallic vapor phase epitaxy are reported in this communication. The magnetic field‐dependent Hall effect measurement was used to characterize the sheet carrier density and electron mobility of the two‐dimensional electron gas (2‐DEG). At 77 K the sheet carrier density and the electron mobility were 1.38×1012 cm−2 and 52 900 cm2 /V s, respectively, in a DHHEMT structure with an undoped Al0.28Ga0.72As spacer layer of 120 A, while they were 7.12×1011 cm−2 and 65 100 cm2 /V s, respectively, in a comparable single‐heterojunction HEMT structure. DHHEMT’s with 0.5‐μm‐gate length and 75‐μm‐gate width have been fabricated with dc saturation current of 500 mA/mm and dc transconductance of 250 mS/mm. These results are comparable to those produced with molecular‐beam epitaxy.

Design and process development of a novel multi-wafer OMVPE reactor for growing very uniform GaAs and AlGaAs epitaxial layers

A unique multi-wafer OMVPE reactor with capability to produce atomic-layer abrupt-ness is demonstrated. Uniform GaAs and AlGaAs epitaxial layers were grown on four two-inch wafers or one three- or four-inch wafer. Thickness variation across a three-inch wafer was less than ±2%, while the variation of Al solid composition was less than ±1%. Multiple AlGaAs/GaAs quantum wells ranging in size from 10Å to 140Å were grown with heterointerface roughness less than one monolayer. The electrical properties of HEMT device were studied. Variations of sheet carrier concentration and electron mobility were ±6% and ±5% respectively across a three-inch wafer. The carrier con-centration profile, mobility spectrum and device characteristics of DH-HEMT are also presented. These results indicate that this OMVPE reactor can grow good device struc-tures for microwave and millimeter-wave power device applications.

The role of lattice matching in improving the performance of PbSnTe IR photodiodes

The role of lattice matching in determining the quantum efficiency of heterostructure PbSnTe photodiodes has been investigated. It has been established that a mismatch of less than 2 × 10-4results in a photodiode with quantum efficiency of ∼ 43%, very close to the maximum 50% possible without an anti-reflection coating. This compares with a value of 28% reported in the case of a heterojunction with a mismatch of 4 × 10-3. The increase in the quantum efficiency is attributed to the high crystalline quality at the heteroface and its vicinity in the lattice-matched system, in contrast to a high defect density found in the mismatched system.