N. E. Schumaker

Continuously operated (Al,Ga)As double‐heterostructure lasers with 70 °C lifetimes as long as two years

Lifetimes longer than two years, and decreases in light output power less than 15% at constant current after one year, both at 70 °C, are reported for selected continuously operated double‐heterostructure (Al,Ga)As lasers. Also, a median 70 °C lasing lifetime of 4500 h is reported for 100 lasers chosen randomly from 10 slices. This median lifetime is thought to correspond to 3.0×105 h (34 yr) of continuous operation had the devices been operated at 22 °C. The corresponding mean time to failure is 1.3×106 h (≳100 yr).

Effects of Ga(As,Sb) active layers and substrate dislocation density on the reliability of 0.87‐μm (Al,Ga)As lasers

Reliability data are presented for (Al,Ga)As double‐heterostructure lasers that emit light near 0.87 μm. Devices were grown with and without small additions of Sb to the active layer, with some devices grown on high dislocation density substrates. The reliability is more than an order of magnitude better for lasers with GaAs1−ySby active layers with y≊0.01 than for lasers with GaAs active layers. The rate of formation of dark line defects is reduced in the Ga(As,Sb) active layer lasers such that not all devices fail due to dark line defects. However, for Ga(As,Sb) active layer lasers grown on high dislocation density substrates, dark line defects formed very rapidly. An increase of roughly an order of magnitude in the substrate dislocation density resulted in a nearly three orders of magnitude decrease in the 70 °C lifetimes of Ga(As,Sb) active layer lasers.

Singular instabilities on LPE GaAs, CVD Si, and MBE InP growth surfaces

Singular instabilities at crystal growth interfaces of group‐IV and III‐V semiconductors lead to as‐grown surfaces optical devices, however, requirethe achievement of smoth planar layers. We consider the stability of surfaces with respect to singular instabilities and show that stable planar growth interfaces occur at slight deviati8ons from the singular orientation where monatomic growth steps are uniformly arrayed to minimize the interfacial energy resulting from step‐step attractive interactions. These results are applied to the elimination of crystal growth terraces in LPE AlGaAs‐GaAs laser material. Similar considerations appear to explain pyramid formations on CVD Si and on MBE InP.

Capacitance spectroscopy studies of degraded AlxGa1−xAs DH stripe‐geometry lasers

The deep‐level transient capacitance spectroscopy (DLTS) technique has been used to study changes in double‐heterostructure (DH) AlxGa1−xAs proton‐bombarded stripe‐geometry lasers during accelerated aging at 70 °C. The DLTS spectra of these lasers consist of three dominant peaks: two shallow traps with activation eneriges of 0.31 eV (majority carrier trap) and 0.21 eV (minority carrier trap) and a deep majority carrier trap with an activation energy of 0.89 eV. The deep trap signal changes dramatically during the first 100 h of cw laser operation at 70 °C, while the two shallow traps change in concentration by only about 10–20%. This deep trap signal increases by over an order of magnitude in lasers of moderate reliability (∼103 h at 70 °C) but is observed to decrease in lasers with very long lifetimes. It is shown that this deep level is introduced by the proton damage and is initially located at the interface between the proton‐damaged layer and the N‐ternary waveguide layer. Finally, studies of the shi...

Laser‐excited photoluminescence of three‐layer GaAs double‐heterostructure laser material

The successful fabrication of high‐quality DH GaAs lasers from a simplified three‐layer structure is reported. A major asset of this structure is the transparency of its final layer to recombination radiation occurring in the active layer, thus permitting the use of nondestructive photoluminescent techniques for material evaluation prior to device fabrication. In the course of photoluminescence investigations on this material the additional important observation has been made that indirect excitation (in which photocarriers are generated in the top ternary layer) has significant advantages over direct excitation (in which photocarriers are generated directly in the active layer). These include (i) the direct measurement of Al concentrations in both upper layers, (ii) the measurements of the minority‐carrier diffusion length in the upper layer, (iii) an easily obtained indication of taper in the thickness of the upper layer, and (iv) surprisingly effective excitation of the active layer. By combining direc...

Photoluminescence measurements in Ge‐doped p‐type Ga0.60Al0.40As

Results of photoluminescence and Hall effect measurements of p‐type Ge‐doped Ga0.60Al0.40As grown by liquid phase epitaxy are reported. The effective segregation coefficient for Ge for growth at 785 °C is estimated to be ∼2×10−3. The photoluminescence spectra at 5.5 K are characterized by two edge emission bands at ∼1.91 and ∼1.88 eV and a broadband at ∼1.55 eV. The edge emission bands are identified to be donor‐acceptor pair recombination bands involving the same donor but two different acceptors. The ionization energy of the donor is estimated to be 50–60 meV and the acceptor ionization energies are estimated to be ∼60 and ∼100 meV for the 1.91‐ and 1.88‐eV bands, respectively. The deep acceptor is believed to involve a background impurity, most likely C or Si. It is suggested that the 1.55‐eV band arises from a next‐nearest neighbor complex consisting of Ge on an arsenic site and an As vacancy. Post‐growth annealing treatment at 830 °C is found to decrease the photoluminescence intensity suggesting the...

Photoluminescence measurements in Ge-doped p-type Ga/sub 0. 60/Al/sub 0. 40/As

Results of photoluminescence and Hall effect measurements of p‐type Ge‐doped Ga0.60Al0.40As grown by liquid phase epitaxy are reported. The effective segregation coefficient for Ge for growth at 785 °C is estimated to be ∼2×10−3. The photoluminescence spectra at 5.5 K are characterized by two edge emission bands at ∼1.91 and ∼1.88 eV and a broadband at ∼1.55 eV. The edge emission bands are identified to be donor‐acceptor pair recombination bands involving the same donor but two different acceptors. The ionization energy of the donor is estimated to be 50–60 meV and the acceptor ionization energies are estimated to be ∼60 and ∼100 meV for the 1.91‐ and 1.88‐eV bands, respectively. The deep acceptor is believed to involve a background impurity, most likely C or Si. It is suggested that the 1.55‐eV band arises from a next‐nearest neighbor complex consisting of Ge on an arsenic site and an As vacancy. Post‐growth annealing treatment at 830 °C is found to decrease the photoluminescence intensity suggesting the...

Characterization of GaAs films grown by metalorganic chemical vapor deposition

We studied undoped GaAs films grown by metalorganic chemical vapor deposition in a vertical geometry atmospheric pressure reactor. Our results on the surface morphology, carrier concentration and conductivity type and low‐temperature photoluminescence spectra of the films, studied as a function of substrate temperature and As/Ga flux during growth, are generally in agreement with previous studies. In addition, we also report the effect of rotation speed of the substrate during growth. It is found that lower speeds give higher defect density and less n‐type films and most notably enhance a defect exciton line at 1.5119 eV. From the free‐to‐bound transitions and from the dependence of the intensities of the exciton lines on growth temperature and As/Ga flux we inferred that the acceptors in our films are C, Zn, Mg and donors are those substituting on Ga sites.

Compensation in Ge‐doped p‐type Ga1−xAlx As grown by liquid phase epitaxy

The effect of compensation on the pair spectra from Ge‐doped p‐type Ga0.60 Al0.40 As grown by liquid‐phase epitaxy under high‐purity He ambient is investigated. It is found that when the amount of compensation is high, pair transitions occur mainly via the deep GeAs acceptors at low excitation levels. The addition of oxygen (0.3–0.9 ppm) or H2 (11%) to the He ambient during growth reduces the compensation, with hydrogen found to be more effective than O2. For reduced compensation, pair transitions via the shallow acceptors due to residual C and Si are favored. The compensation is due to the presence of residual donors such as S whose concentration varies from wafer to wafer causing fluctuations in the relative intensities of pair transitions. Since strong pair transitions involving shallow acceptors reflect low concentration of compensating donors and thus improved conductivity in the p layers, the use of H2 in the He ambient gas during the growth of (GaAl)As double‐heterolaser structures should be advant...

Gallium phosphide beam lead electroluminescent devices

Beam lead GaP electroluminescent diodes have been developed using a quasi-planar configuration. This new structure couples the advantages of beam lead technology to the high-efficiency GaP p-n junctions prepared by liquid phase epitaxial (LPE) growth. The devices consist of a p-type (Zn, O-doped) LPE mesa formed on an n-type (Te-doped) LPE layer grown on an n-type Czochralski-grown substrate. A deposited insulator film covers the entire mesa surface and passivates the exposed junction perimeter. Ohmic contacts are made to both the p- and n-regions through holes in the insulating layer and beam leads are applied by conventional technology. The finished devices are shaped into domed structures during the final separation of the wafer into individual devices. Complete devices bonded to substrates were operated at 10 mA with typical forward voltages of 1.95 ± 0.05 V with external quantum efficiencies of 2-2.25 per cent (unencapsulated). This beam lead quasi-planar structure takes advantage of the inherently large size of the individual devices dictated by optical considerations and allows a number of improvements in device design. The areas where advantages over existing GaP diodes can be realized are as follows, 1) Optimization of external efficiency by contact design and diode configuration is possible. 2) Planar beam lead processing and junction passivation methods can be used, 3) Array fabrication in discrete or monolithic forms is feasible.