IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. ED-28, NO. 10, OCTOBER 1981 1221

output of a variety of surface and edge- emitting device structures in the temperature range 77-400K will be presented. Particular emphasis will be given to those aspects of device structure, such as confining and active layer compositions, thicknesses and doping levels, which have major effects on the overall device performance.

Surface emitters are generally much less temperature dependent (-dL/dT - 0.15 - 0.4% K-') than are edge emitters (-dL/dT - 0.5 - 1% IC'), at least in the temperature range 200-400K. Although it might be assumed that these differences are due to the higher internal absorption of the light in edge-emitters, as it propagates to the emitting facet, experimental results will be shown which demonstrate that this is not the case. Instead, a model which invokes a temperature dependent in-plane superluminescence will be shown to be capable of describing the experimental data.

It will also be demonstrated that careful tailoring of the basic double heterostructure enables surface emitters to be prepared with an essentially temperature invariant light- current characteristic in the temperature range 250-350K. Such devices have obvious applications, not only in fibre optical transmission systems transmitters which are not maintained in a thermally stable environment, but in standardization apparatus. These device concepts are now being applied to GaInAsP/InP surface emitters for similar immediate applications.

IIIA-2 Hot Carrier Effects in 1.3 pm Inl,GaxAs,,P1, LEDs-R. E. Nahory, J. Shah, R. F. Leheny, and H. T. Temkin, Bell Laboratories, Holmdel, NJ 07733.

We report significant hot carrier effects for Inl-,GaxAsyP1, 1.3 p m LEDs operating at typical current levels. Carrier temperatures as high as 400K are found for diodes operating at room temperature ambient. It is well known that LEDs fabricated from these alloy materials exhibit sublinear dependence on drive current.' Further, lasers fabricated from similar alloy

materials exhibit large temperature sensitivity of threshold current and quantum efficiency.' Recently, model calculations have been reported that attempt to explain these characteristics in terms of processes such as Auger recombination or intervalence band absorption and assuming carrier temperature equal to lattice temperatures. In this work we demonstrate through analysis of electroluminescence spectra that this assumption is incorrect and show that carrier temperature is significantly higher than the lattice at typical operating conditions. Our measurements are made on 1.3 p m surface emitting LEDs at drive currents ranging from 10 mA to 250 mA and ambient temperatures ranging from lOOK to 300K. Over the entire temperature range, we find significant carrier heating effects. The variation of carrier heating with ambient temperature demonstrates that the energy input to the carriers responsible for this heating is reduced at low ambient temperatures. The present measurements provide information on the final carrier distribution, but cannot as yet distinguish between possible hot carrier generation mechanisms. However, regardless of the sources of energy heating the carriers, our results demonstrate the importance of taking hot carrier effects into account.

*Bell Laboratories, Murray Hill, New Jersey.

'R. C. Goodfellow, et al., 37th DRC paper TP-66 (1979) and papers at 4th IEEE Conf. on Tech. Electroluminescence Diodes, Brighton, England, (1980).

'G. H. B. Thompson and G. D. Henshall, paper P50 (and post deadline papers), 7th IEEE Intern. Semiconductor Laser Conf., Brighton, England, (1980).

IIIA-3 The To-Problem of GaInAsP/TnP- Lasers: Investigations by Optical Gain Spectroscopy+- E. 0. Gobel*, H. Jung, K. M. Romanek, A. Mozer, and M. €3. Pilkuhn, Physikalisches Institut, Universitat Stuttgart, D-7000, Stuttgart 80.

1222 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. ED-28, NO. 10, OCTOBER 1.981

'Max-Planck-Institut fur Festkorperforschung, D-7000, Stuttgart 80.

Long wavelength GaInAsP/InP-lasers show an unusually strong temperature dependence of the threshold current density described by a small characteristic temperature To in the exponential relation

two or even three To-values have to be assumed to described the threshold behaviour. As Physical reasons for the small To-values e.g. nonradiative recombination, intervalence band absorption and leakage currents have been suggested.

TITO j t h - e ("To-problem"). Furthermore,

We report optical gain experiments on GaInAsP/InP-double heterostructures (DHS) in the temperature range from 80K to 300K. The temperature dependence of the maximum gain, g,,,, is compared with threshold measurements of DHS-injection lasers which we have fabricated from the same wafer. We find an identical behaviour of the temperature dependence of g,,, and j,,, i.e. the To-values as well as the "breakpoint" temperature are the same in both cases (To = 95K for T < 260K; TO = 62K for T > 260K). This demonstrates that the To-problem is an intrinsic property of the laser waveguide. For more insight into the threshold behaviour we have also analyzed the spectral shape of the optical gain. We find that the optical gain does not correspond to a simple band to band transition, but exhibits two spectral bands separated by 5 to 15 meV. The gain spectra are temperature dependent: At low temperature the low energy gain prevails, at high temperature the high energy gain band is strongest. It is of particular interest, that the gain maximum shifts from the low energy band to the high energy band exactly at the "breakpoint" temperature. These new observations will be supplemented by recent data on the saturation behaviour of high radiance GaInAsP-LEDs and their spectral properties.

'Research support by the German Research Association DFG.

IIIA-4 A Comparison of Temperature Dependence of Lasing Characteristics of 1.3 p m InGaAsP and GaAs DH Lasers-N. K. Dutta and R. J. Nelson, Bell Laboratories, Murray Hill, NJ 07974.

The 1.3 bm InGaAsP-InP double heterostructure (DH) lasers are promising devices for use in future light wave communication systems. One of the major differences between this system and the GaAs-A1.36Ga.64As DH Lasers is its high temperature sensitivity of threshold current.'

We report here our experimental observations on temperature dependence of threshold current, carrier lifetime at threshold and gain of both the 1.3 pm InGaAsP and GaAs DH lasers. We find that the gain decreases much faster with increasing temperature for a 1.3 p m InGaAsP DH laser than for a GaAs DH laser. Measurements of the spontaneous emission observed through the substrate shows that the emission is sublinear with injection current at high temperatures for the 1.3 pm InGaAsP DH lasers. Such sublinearity is not observed for GaAs DH lasers in the entire temperature range 115- 350K. These observations can be explained by a nonradiative Auger recombination mechanism which is important for the InGaAsP material.' Experimental results at higher injection levels over a range of temperatures show a sublinear behavior in both GaAlAs and InGaAsP LEDs. This observation can be interpreted in terms of an additional single pass optical gain which is present at high injection levels.

An improved calculation of the threshold current density and carrier lifetime at threshold using fundamental band structure parameters is presented. The calculation is done using Halperin-Lax-Kane band model, Stern's matrix element and modified Beattie-Landsberg theory of Auger recombination. The Auger recombination rate for various band to band and phonon assisted processes are calculated taking into account nonparabolicity of the bands, Fermi statistics and screening effects. We find that the calculated nonradiative Auger recombination rate is significant at high temperatures for the InGaAsP material.