V. G. Keramidas

Deep radiative levels in InP

Results of a detailed photoluminescence study of deep radiative transitions in InP crystals prepared by the bulk and epitaxial techniques are reported. In order to understand the origin of the photoluminescence (PL) spectra, bulk samples were subjected to isothermal anneals at different partial pressures of phosphorus. Similarly, the liquid phase epitaxy (LPE) wafers were grown with and without phosphorus in the gas stream. The electrical nature of some of the species responsible for the PL emission was inferred by a study of Cd diffused bulk samples. Based on these experiments the following tentative assignments are proposed. The photoluminescence band at 0.99 eV, common to all samples, is due to emission from a donorlike level related to the P vacancy. Bands at 1.21 and 1.14 eV appear to be due to emission to native acceptor levels associated with the In vacancy. The 1.08‐eV band is attributed to emission to a complex of the donor (0.99 eV) and acceptor (1.21 eV) species. The relationship between these ...

Ohmic contacts to p‐type InP using Be‐Au metallization

A new contact to p‐InP is reported with beryllium as the acceptor. The contact consists of a thin layer of 3 wt.% Be in Au alloy and a Au overlay sequentially deposited by e‐gun evaporation. Alloying at 420 °C yields Ohmic contacts with low specific contact resistance rc⩽8×10−5 Ω cm2 for InP with NA−ND ≲1×1018 cm−3. To minimize the tendency of InP for thermal dissociation, the alloying temperature can be reduced to 375 °C by adding a thin Pd layer at the semiconductor metallization interface. This is achieved at the expense of a slight increase in resistance.

Transport properties of selectively doped GaAs‐(AlGa)As heterostructures grown by molecular beam epitaxy

In selectively doped GaAs‐(AlGa)As heterostructures the two‐dimensional (2D) electron density is found to be monotonically decreasing with increasing separation (t0) between the mobile carriers and the doped (AlGa)As layer. A quantitative description of this t0 dependence requires the Si dopant to create a deep center in (Al0.3Ga0.7)As. For t0≳60 A the low‐temperature electron mobility, which can be as high as 1.6×106 cm2/Vs, does not show a correlation with t0. Unidentified and as yet uncontrollable impurities in the vicinity of the 2D system are a likely source for the residual electron scattering.

Ohmic contact to p-type InP

An ohmic contact to a semiconductor device comprising p-type InP is formed by sequentially depositing beryllium-gold and gold layers on InP and then heat-treating the device at a temperature less than 440 degrees C. An ohmic contact to p-type InGaAsP can be similarly formed.

Light‐current characteristics of InGaAsP light emitting diodes

Light‐current characteristics of 1.3‐μm InGaAsP light emitting diodes were investigated as a function of temperature between 70 and 350 K. The sublinearity of the light output found at high injection levels was shown to be temperature independent and similar in magnitude to that observed in GaAlAs devices. These experimental results cannot be explained with the previously proposed models of in‐plane superluminescence and Auger recombination.

Manifestations of melt‐carry‐over in InP and InGaAsP layers grown by liquid phase epitaxy

Macroscopic evidence for the occurrence of melt‐carry‐over (MCO) in InP and InGaAsP layers, grown by liquid phase epitaxy, is presented. It is shown that MCO can manifest itself in the form of dissolution pits and holes in epilayers. Further, this carry‐over can occur in any stage of epi growth and can propagate through subsequent epitaxial layers. Thus, holes transcending all four layers constituting a device wafer can form if wipe‐off after an In‐melt back is incomplete, and these holes have deleterious effects on device yield.

Perfection of homoepitaxial layers grown on (001) InP substrates

The perfection of homoepitaxial layers grown on highly S‐, Zn‐ and Sn‐doped InP substrates by liquid phase epitaxy has been evaluated by etch pitting and transmission cathodoluminescence. It is shown that high‐quality layers, which are macroscopically dislocation free over large areas, can be grown on the S‐doped substrates. The situation regarding the epitaxial layers deposited on the Zn‐doped substrates is complex. The transmission cathodoluminescence study reveals, in addition to dislocations, areas with poor luminescence within the epitaxial layers. Furthermore, the quality of thin layers (∼2 μm thick) grown on the Zn‐ and Sn‐doped substrates is better than that of the thick layers (∼10 μm).

Competing processes in long term accelerated aging of double heterostructure Ga1−xAlxAs light emitting diodes

Two competing processes have been observed in bias aging of double heterostructure (DH) Ga1−xAlxAs light emitting diodes (LEDs) at elevated temperatures. These high radiance LEDs are used as sources in optical data links. In the past, only a single aging process, slow degradation in light output, has been reported for dark line defect (DLD)‐free LEDs of similar type. In contrast, we report for the first time, a second process which gives a gradual increase in light output. As temperature and current are increased this new process increasingly masks the degradation process, until at 270 °C there is a net increase in light output of 50% after about 300 h of aging. We show that the two processes have different time dependences and activation energies, and that their effects on the light output during aging can be separated mathematically. A model for the new process is presented in which nonradiative traps anneal out in a recombination‐enhanced defect reaction. This leads to higher injection efficiency and light output at fixed current. Operating lifetimes increase due to the second process; for example, at 25 °C mean‐time‐to‐failure (MTTF) increases by a factor of three to 9×107 h.Two competing processes have been observed in bias aging of double heterostructure (DH) Ga1−xAlxAs light emitting diodes (LEDs) at elevated temperatures. These high radiance LEDs are used as sources in optical data links. In the past, only a single aging process, slow degradation in light output, has been reported for dark line defect (DLD)‐free LEDs of similar type. In contrast, we report for the first time, a second process which gives a gradual increase in light output. As temperature and current are increased this new process increasingly masks the degradation process, until at 270 °C there is a net increase in light output of 50% after about 300 h of aging. We show that the two processes have different time dependences and activation energies, and that their effects on the light output during aging can be separated mathematically. A model for the new process is presented in which nonradiative traps anneal out in a recombination‐enhanced defect reaction. This leads to higher injection efficiency and l...

Growth of InP and InGaAsP (Eg≥1.15 eV) layers by liquid phase epitaxy under phosphorus overpressure

A method is presented for the liquid phase epitaxial growth of stoichiometric InP and InGaAsP (Eg⩾1.15 eV) epitaxial layers by creating a phosphorus overpressure in the growth ambient. The effectiveness of the method and the stoichiometry of InP layers can be monitored with the photoluminescent spectra of a phosphorus vacancy‐impurity complex.

Comparative Study Of GaAs Grown By Organometallic Chemical Vapor Deposition (OMCVD) Using Trimethyl And Triethyl Gallium Sources

Atmospheric and low pressure (76 torr) epitaxial growth of gallium arsenide (GaAs) from trimethyl gallium (TMG) and triethyl gallium (TEG) has been studied. The results indicate that both TMG and TEG are capable of yielding high purity GaAs epitaxial layers. TMG is the preferred compound when large area uniform layers are desired at all reactor pressures. TEG is recommended only in those cases where carbon acceptor free GaAs is required and low pressure capability is available.